Stabilized matrix-filled liquid radiation curable resin compositions for additive fabrication

ABSTRACT

Matrix-filled liquid radiation curable resin compositions for additive fabrication are described and claimed. Such resins include a cationically polymerizable component that is an aliphatic epoxide, a multifunctional (meth)acrylate component, a cationic photoinitiator, a free-radical photo initiator, and a matrix of inorganic fillers, wherein the matrix further constitutes prescribed ratios of at least one microparticle constituent and at least one nanoparticle constituent. Also described and claimed is a process for using the matrix-filled liquid radiation curable resins for additive fabrication to create three dimensional parts, and the three-dimensional parts made from the liquid radiation curable resins for additive fabrication.

TECHNICAL FIELD

The present invention relates to matrix-filled liquid radiation curablecompositions for additive fabrication processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Applications No.61/900,044 filed 5 Nov. 2013 and No. 62/074,735 filed 4 Nov. 2014, eachof which are hereby incorporated by reference in their entirety as iffully set forth herein.

BACKGROUND

Additive fabrication processes for producing three dimensional objectsare well known. Additive fabrication processes utilize computer-aideddesign (CAD) data of an object to build three-dimensional parts. Thesethree-dimensional parts may be formed from liquid resins, powders, orother materials.

A non-limiting example of an additive fabrication process isstereolithography (SL). Stereolithography is a well-known process forrapidly producing models, prototypes, patterns, and production parts incertain applications. SL uses CAD data of an object wherein the data istransformed into thin cross-sections of a three-dimensional object. Thedata is loaded into a computer which controls a laser that traces apattern of a cross section through a liquid radiation curable resincomposition contained in a vat, solidifying a thin layer of the resincorresponding to the cross section. The solidified layer is recoatedwith resin and the laser traces another cross section to harden anotherlayer of resin on top of the previous layer. The process is repeatedlayer by layer until the three-dimensional object is completed. Wheninitially formed, the three-dimensional object is, in general, not fullycured, and is called a “green model.” Although not required, the greenmodel may be subjected to post-curing to enhance the mechanicalproperties of the finished part. An example of an SL process isdescribed in U.S. Pat. No. 4,575,330, which is hereby incorporated byreference.

There are several types of lasers used in stereo lithography,traditionally ranging from 193 nm to 355 nm in wavelength, althoughother wavelength variants exist. The use of gas lasers to cure liquidradiation curable resin compositions is well known. The delivery oflaser energy in a stereolithography system can be Continuous Wave (CW)or Q-switched pulses. CW lasers provide continuous laser energy and canbe used in a high speed scanning process. However, their output power islimited which reduces the amount of curing that occurs during objectcreation. As a result the finished object will need additional postprocess curing. In addition, excess heat could be generated at the pointof irradiation which may be detrimental to the resin. Further, the useof a laser requires scanning point by point on the resin which can betime-consuming.

Other methods of additive fabrication utilize lamps or light emittingdiodes (LEDs). LEDs are semiconductor devices which utilize thephenomenon of electroluminescence to generate light. At present, LED UVlight sources currently emit light at wavelengths between 300 and 475nm, with 365 nm, 390 nm, 395 nm, 405 nm, and 415 nm being common peakspectral outputs. See textbook, “Light-Emitting Diodes” by E. FredSchubert, 2^(nd) Edition, © E. Fred Schubert 2006, published byCambridge University Press, for a more in-depth discussion of LED UVlight sources.

Many additive fabrication applications require a freshly-cured part, akathe “green model” to possess high mechanical strength (modulus ofelasticity, fracture strength). This property, often referred to as“green strength,” constitutes an important property of the green modeland is determined essentially by the nature of the liquid radiationcurable resin composition employed in combination with the type ofapparatus used and degree of exposure provided during part fabrication.Other important properties of a stereolithographic resin compositioninclude a high sensitivity for the radiation employed in the course ofcuring and a minimum amount of curl or shrinkage deformation, permittinghigh shape definition of the green model. Of course, not only the greenmodel but also the final cured article should have sufficientlyoptimized mechanical properties.

For select additive fabrication applications in the aerospace orautomotive industries, for example, three-dimensional solid parts aresubjected to the high force loads of a wind tunnel, or the extremetemperatures of a location proximate to heat-generating componentry. Insuch applications, designers and engineers require a three-dimensionalsolid part created via additive fabrication to maintain its structuralintegrity and minimize deflection. Thus three-dimensional parts madefrom photopolymerizable compositions must possess ceramic-like materialproperties, such as high strength, stiffness, and heat resistance.

“Filled” liquid radiation curable resins have long been used in thefield in an attempt to meet these specialized application designcriteria. That is, high amounts of inorganic filler, such as silica(SiO₂) have been imparted into traditional “unfilled” liquid radiationcurable resins due to the filler's positive impact on the strength andstiffness of the three-dimensional object produced therefrom. Suchfilled liquid radiation curable compositions are known in the art ofadditive fabrication, and are disclosed in, e.g., U.S. Pat. No.5,972,563 (Issued Oct. 26, 1999), U.S. Pat. No. 5,989,475 (Issued Nov.23, 1999), U.S. Pat. No. 6,287,745 (Issued Sep. 11, 2001), U.S. Pat. No.6,742,456 (Issued Jun. 1, 2004), U.S. Pat. Pub. No. 20020045126, U.S.Pat. Pub. No. 20040077745, and U.S. Pat. Pub. No. 20050101684, all ofwhich are hereby incorporated by reference. While the aforementionedpatents disclose fundamental filled liquid radiation curablecompositions, none discuss or teach compositions sufficiently andsimultaneously overcoming the several drawbacks typically associatedwith their use.

Thus, highly filled compositions present several challenges to theformulator of liquid radiation curable resins for additive fabrication.Heretofore no filled liquid radiation curable composition for additivefabrication existed that could both yield three-dimensional partspossessing excellent mechanical properties, yet simultaneously avoid:(1) a high initial viscosity, (2) a poor viscosity stability, and (3) atendency to phase separate, resulting in phenomena known as either “softpack” or “hard pack.”

The first long-felt problem with filled liquid radiation curable resincompositions for additive fabrication is that as the amount of fillerincreases, the viscosity of the resin also usually increases, resultingin decreased workability and processing speed. Highly viscous resinsparticularly retard the processing speed in vat-based additivefabrication systems such as stereolithography. Existing resins aresufficiently flow-resistant such that they will not readily form asmooth layer of liquid photo curable resin over the just formed solidlayer to ensure accurate cure by actinic radiation. Consequently, arecoating operation has traditionally been used to simultaneously placeand mechanically smooth a fresh layer of resin over a previously curedlayer prior to exposure with actinic radiation. In one non-limitingexample, this recoating operation has traditionally been performed bymeans of a “recoating blade.” A recoating blade design is discussed in,for example, Chapman et al., U.S. Pat. No. 5,626,919, assigned to DSM IPAssets, B.V.

Even with a recoating operation, however, low viscosity remains animportant characteristic of the resin. The filled liquid radiationcurable resin composition's viscosity affects the time it takes toequilibrate as a smooth, even surface after the recoating step.Consequently, a programmed “dwell time” has been traditionally usedbetween the end of the recoating operation and the beginning of theexposure of the next layer of resin to appropriate imaging radiation.Both the recoating operation and the dwell time dramatically increasethe process time of a typical vat-based additive fabrication process.

Additionally, the viscosity of the liquid radiation curable resin alsoaffects the time and difficulty associated with preparing arecently-cured part for post processing operations. In a vat-basedadditive fabrication process, upon build completion of athree-dimensional solid part, the solidified portions are removed fromthe liquid uncured resin. A highly viscous resin will be more difficultto separate from the cured part, wherein a resin of substantially lowviscosity will be removed without significant effort. Thus, lowviscosity resins reduce the time required to clean a part in order toprepare it for post processing operations.

Second, while the importance of filled liquid radiation curablecompositions for additive fabrication with a sufficiently low initialviscosity is significant, it is equally as important to conduct additivefabrication processes with a resin having sufficient viscosity stabilityover time. Filled liquid radiation curable resins for additivefabrication possess a well-known amplified tendency to increase inviscosity over time than versus traditional unfilled resins. Thisexacerbates the aforementioned problems associated with the high initialviscosities of filled compositions, resulting in increasingly lessefficient, more costly additive fabrication processes over time.

Additionally, highly filled compositions are usually not as thermal- orphoto-stable as non-filled liquid radiation curable resins for additivefabrication. Photo stability is the ability of a liquid radiationcurable resin to maintain its viscosity after exposure to ambient lightand undesirable light scattering in additive fabrication machines.Thermal stability is the ability of a liquid radiation curable resin tomaintain its viscosity after exposure to elevated temperatures, whichare known to accelerate cationic polymerization. Because liquidradiation curable resins for additive fabrication include reactivespecies that are responsive to undesirable ambient light scattering thatoccurs as a result of contact with crystallized filled particles,partial uncontrolled polymerization occurs in the liquid radiationcurable resin after it is exposed to light. This small amount ofuncontrolled polymerization, over time, is accelerated if the resin isstored at elevated temperatures. These factors cause the viscosity ofthe liquid radiation curable resin to increase gradually—butsignificantly—over time. Thus achieving sufficient viscosity stabilityis particularly challenging in highly filled liquid radiation curableresins because of additional light scattering effects caused by thefiller.

A third problem traditionally associated with filled liquid radiationcurable compositions for additive fabrication is their tendency to phaseseparate in storage or a vat over time. This phase separation, wherebythe inorganic filler loses its state of homogeneous suspension in thesurrounding liquid radiation curable resin, results in a vat made up ofa bifurcated composition: (1) a low-viscosity, largely unfilled topportion, and (2) a supersaturated, high-viscosity bottom portion. Theresin in the top portion of a vat is not able to produce cured partspossessing sufficient strength and stiffness (because of a lack offilled component present in the composition), while the bottom portionis devoid of any suitability for additive fabrication at all (due to anexcess of filled particles). Despite the historical inclusion ofinorganic particles designed for anti-sedimentation, existing filledliquid radiation curable compositions for additive fabricationinvariably eventually settle, either into a “soft pack” or a “hardpack.” In the more benign settling phenomenon, a soft pack, the settledfiller forms a waxy portion at the bottom of a storage container or vat.The settled filler is frequently surrounded by partially polymerizedresin, resulting in the wax-like consistency. Although re-assimilationinto the liquid radiation curable resin as a whole is possible, itrequires frequent and often vigorous recirculation. This is a time- andenergy-consuming maintenance process, and still does not obviate aresin's eventual viscosity increase, due to the rampant partialpolymerization.

Still other filled liquid radiation curable compositions for additivefabrication settle into an undesirable “hard pack.” Hard pack occurswhereby the inorganic filler settles to the bottom of a storagecontainer or vat, forming a concrete-like piece or pieces. These piecesmust be broken up by a drill or similar apparatus, and are typicallyunable to be re-assimilated into the liquid radiation curable resin as awhole. This shortens the shelf-life of such resins, or results inchanging and inconsistent properties in the cured parts made therefrom,due to the changing amounts of filler component which are notre-miscible into the solution. Thus, it is especially desirable toformulate a liquid radiation curable resin composition for additivefabrication which, in addition to the other required performancecharacteristics mentioned above, possesses superior anti-sedimentationcapabilities.

Various other patents or patent publications also describe usinginorganic filled compositions comprising, inter alia, silicamicroparticles and/or nanoparticles, among them:

U.S. Pat. No. 6,013,714 (Haruta et al.), assigned to DSM IP Assets,B.V., which describes additive fabrication processes that utilizesfilled resins to performing a combination of steps, including (1)applying a thin layer of resin on a supporting stage; (2) selectivelyirradiating the thin layer of resin as to cure a selected part of saidresin; (3) applying a further thin layer of resin; and repeating steps(2) and (3) as to obtain a three dimensional shape of a plurality ofcured layers, optionally combined with either one of the steps ofwashing and post-curing the three dimensional shape, as to obtain themold, wherein the resin composition is formulated from constituentscomprises at least one photoreaction monomer at least one photoinitiatorat least one filler.

U.S. Pat. Pub. No. 20050040562 (Steinmann et al.), assigned to 3DSystems, Inc., which describes a process for forming a three-dimensionalarticle by stereolithography, said process comprising the steps: 1)coating a thin layer of a liquid radiation-curable composition onto asurface of said composition including at least one filler comprisingsilica-type nano-particles suspended in the radiation-curablecomposition: 2) exposing said thin layer imagewise to actinic radiationto form an imaged cross-section, wherein the radiation is of sufficientintensity to cause substantial curing of the thin layer in the exposedareas; 3) coating a thin layer of the composition onto the previouslyexposed imaged cross-section; 4) exposing said thin layer from step (3)imagewise to actinic radiation to form an additional imagedcross-section, wherein the radiation is of sufficient intensity to causesubstantial curing of the thin layer in the exposed areas and to causeadhesion to the previously exposed imaged cross-section; 5) repeatingsteps (3) and (4) a sufficient number of times in order to build up thethree-dimensional article.

U.S. Pat. Pub. No. 20120251841 (Southwell et al.), assigned to DSM IPAssets B.V., which describes liquid radiation curable resins foradditive fabrication comprising an R-substituted aromatic thioethertriaryl sulfonium tetrakis(pentafluorophenyl)borate cationicphotoinitiator and silica nanoparticles. Also disclosed is a process forusing the liquid radiation curable resins for additive fabrication andthree-dimensional articles made from the liquid radiation curable resinsfor additive fabrication.

From the foregoing, it is evident that no filled liquid radiationcurable compositions for additive fabrication exist that are suitablefor producing cured components having adequate application-specific heatresistance and structural rigidity, while simultaneously overcoming thelong-felt but unsolved industry needs of providing the requisite lowinitial viscosity, high viscosity stability, and high phase-separationresistance.

BRIEF SUMMARY

The first aspect of the claimed invention is a liquid radiation curablecomposition for additive fabrication comprising:

(a) a cationically polymerizable aliphatic epoxide;

(b) a multifunctional (meth)acrylate component;

(c) a cationic photoinitiator;

(d) a free-radical photoinitiator; and

(e) a filled matrix comprising

-   -   a nanoparticle constituent comprising a plurality of inorganic        nanoparticles, and    -   a microparticle constituent comprising a plurality of inorganic        microparticles; wherein the ratio by weight of the microparticle        constituent to the nanoparticle constituent is from about 1:1 to        about 12:1, more preferably from about 4:1 to about 8:1, and        wherein the ratio of the average particle size of the inorganic        microparticles in the microparticle constituent to the average        particle size of the inorganic nanoparticles in the nanoparticle        constituent is from about 2.41:1 to about 200:1, more preferably        from about 6.46:1 to about 100:1.

The second aspect of the claimed invention is a process of forming athree-dimensional object comprising the steps of forming and selectivelycuring a layer of the liquid radiation curable resin compositionaccording to the present invention as described herein with actinicradiation and repeating the steps of forming and selectively curing alayer of the liquid radiation curable resin composition for additivefabrication as described herein a plurality of times to obtain athree-dimensional object.

The third aspect of the claimed invention is the three-dimensionalobject formed from the liquid radiation curable resin of the firstaspect of the present invention by the process of the second aspect ofthe claimed invention.

The fourth aspect of the claimed invention is a liquid radiation curableresin for additive fabrication comprising:

(a) a cationically polymerizable component;

(b) a (meth)acrylate component;

(c) a cationic photoinitiator;

(d) a free-radical photoinitiator; and

(e) a filled matrix, further comprising

-   -   a filled particle dispersion containing        -   a nanoparticle constituent made up of a plurality of silica            nanoparticles having an average particle size of at least            about 50 nanometers, and a solvent, and    -   a microparticle constituent made up of a plurality of inorganic        microparticles; wherein the ratio by weight of the microparticle        constituent to the nanoparticle constituent is from about 1:1 to        about 12:1; and    -   wherein the filled particle dispersion has a particle dispersion        pH of greater than about 5.5.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a two-dimensional cross-sectional view of an embodimentof a square configuration filled matrix of the present invention.

FIG. 2 depicts a two-dimensional cross-sectional view of an embodimentof a triangular configuration filled matrix of the present invention.

DETAILED DESCRIPTION

An embodiment of the claimed invention is a liquid radiation curablecomposition for additive fabrication, comprising:

(a) a cationically polymerizable aliphatic epoxide;

(b) a multifunctional (meth)acrylate component;

(c) a cationic photoinitiator;

(d) a free-radical photoinitiator; and

(e) a filled matrix comprising

-   -   a nanoparticle constituent comprising a plurality of inorganic        nanoparticles, and    -   a microparticle constituent comprising a plurality of inorganic        microparticles; wherein the ratio by weight of the microparticle        constituent to the nanoparticle constituent is from about 1:1 to        about 12:1, more preferably from about 4:1 to about 8:1, and        wherein the ratio of the average particle size of the inorganic        microparticles in the microparticle constituent to the average        particle size of the inorganic nanoparticles in the nanoparticle        constituent is from about 2.41:1 to about 200:1, more preferably        from about 6.46:1 to about 100:1.

Cationically Polymerizable Component

In accordance with an embodiment, the liquid radiation curable resinsfor additive fabrication of the invention comprise at least onecationically polymerizable component; that is a component whichundergoes polymerization initiated by cations or in the presence of acidgenerators. The cationically polymerizable components may be monomers,oligomers, and/or polymers, and may contain aliphatic, aromatic,cycloaliphatic, arylaliphatic, heterocyclic moiety(ies), and anycombination thereof. Suitable cyclic ether compounds can comprise cyclicether groups as side groups or groups that form part of an alicyclic orheterocyclic ring system.

The cationic polymerizable component is selected from the groupconsisting of cyclic ether compounds, cyclic acetal compounds, cyclicthioethers compounds, spiro-orthoester compounds, cyclic lactonecompounds, and vinyl ether compounds, and any combination thereof.

Suitable cationically polymerizable components include cyclic ethercompounds such as epoxy compounds and oxetanes, cyclic lactonecompounds, cyclic acetal compounds, cyclic thioether compounds, spiroorthoester compounds, and vinylether compounds. Specific examples ofcationically polymerizable components include bisphenol A diglycidylether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether,brominated bisphenol A diglycidyl ether, brominated bisphenol Fdiglycidyl ether, brominated bisphenol S diglycidyl ether, epoxy novolacresins, hydrogenated bisphenol A diglycidyl ether, hydrogenatedbisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-1,4-dioxane,bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide,4-vinylepoxycyclohexane, vinylcyclohexene dioxide, limonene oxide,limonene dioxide, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexanecarboxylate,ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylates, trimethylcaprolactone-modified3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylates,β-methyl-δ-valerolactone-modified3,4-epoxycyclohexcylmethyl-3′,4′-epoxycyclohexane carboxylates,methylenebis(3,4-epoxycyclohexane), bicyclohexyl-3,3′-epoxide,bis(3,4-epoxycyclohexyl) with a linkage of —O—, —S—, —SO—, —SO₂—,—C(CH₃)₂—, —CBr₂—, —C(CBr₃)₂—, —C(CF₃)₂—, —C(CCl₃)₂—, or —CH(C₆H₅)—dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl) ether ofethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate),epoxyhexahydrodioctylphthalate, epoxyhexahydro-di-2-ethylhexylphthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidylether, neopentylglycol diglycidyl ether, glycerol triglycidyl ether,trimethylolpropane triglycidyl ether, polyethylene glycol diglycidylether, polypropylene glycol diglycidyl ether, diglycidyl esters ofaliphatic long-chain dibasic acids, monoglycidyl ethers of aliphatichigher alcohols, monoglycidyl ethers of phenol, cresol, butyl phenol, orpolyether alcohols obtained by the addition of alkylene oxide to thesecompounds, glycidyl esters of higher fatty acids, epoxidated soybeanoil, epoxybutylstearic acid, epoxyoctylstearic acid, epoxidated linseedoil, epoxidated polybutadiene,1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene,3-ethyl-3-hydroxymethyloxetane,3-ethyl-3-(3-hydroxypropyl)oxymethyloxetane,3-ethyl-3-(4-hydroxybutyl)oxymethyloxetane,3-ethyl-3-(5-hydroxypentyl)oxymethyloxetane,3-ethyl-3-phenoxymethyloxetane, bis((1-ethyl(3-oxetanyl))methyl)ether,3-ethyl-3-((2-ethylhexyloxy)methyl)oxetane,3-ethyl-((triethoxysilylpropoxymethyl)oxetane,3-(meth)-allyloxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-ethyloxetane,(3-ethyl-3-oxetanylmethoxy)methylbenzene,4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene,4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)methyl]-benzene,[1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether,isobutoxymethyl(3-ethyl-3-oxetanylmethyl)ether,2-ethylhexyl(3-ethyl-3-oxetanylmethyl)ether, ethyldiethyleneglycol(3-ethyl-3-oxetanylmethyl)ether, dicyclopentadiene(3-ethyl-3-oxetanylmethyl)ether,dicyclopentenyloxyethyl(3-ethyl-3-oxetanylmethyl)ether,dicyclopentenyl(3-ethyl-3-oxetanylmethyl)ether,tetrahydrofurfuyl(3-ethyl-3-oxetanylmethyl)ether,2-hydroxyethyl(3-ethyl-3-oxetanylmethyl)ether,2-hydroxypropyl(3-ethyl-3-oxetanylmethyl)ether, and any combinationthereof.

The cationically polymerizable component may optionally also containpolyfunctional materials including dendritic polymers such asdendrimers, linear dendritic polymers, dendrigraft polymers,hyperbranched polymers, star branched polymers, and hypergraft polymerswith epoxy or oxetane functional groups. The dendritic polymers maycontain one type of polymerizable functional group or different types ofpolymerizable functional groups, for example, epoxy and oxetanefunctions.

In an embodiment, the composition of the present invention alsocomprises one or more mono or poly glycidylethers of aliphatic alcohols,aliphatic polyols, polyesterpolyols or polyetherpolyols. Examples ofpreferred components include 1,4-butanedioldiglycidylether,glycidylethers of polyoxyethylene and polyoxypropylene glycols andtriols of molecular weights from about 200 to about 10,000;glycidylethers of polytetramethylene glycol orpoly(oxyethylene-oxybutylene) random or block copolymers. In a specificembodiment, the cationically polymerizable component comprises apolyfunctional glycidylether that lacks a cyclohexane ring in themolecule. In another specific embodiment, the cationically polymerizablecomponent includes a neopentyl glycol diglycidyl ether. In anotherspecific embodiment, the cationically polymerizable component includes a1,4 cyclohexanedimethanol diglycidyl ether.

Examples of commercially available preferred polyfunctionalglycidylethers are Erisys™ GE 22 (Erisys™ products are available fromEmerald Performance Materials™), Heloxy™ 48, Heloxy™ 67, Heloxy™ 68,Heloxy™ 107 (Heloxy™ modifiers are available from Momentive SpecialtyChemicals), and Grilonit® F713. Examples of commercially availablepreferred monofunctional glycidylethers are Heloxy™ 71, Heloxy™ 505,Heloxy™ 7, Heloxy™ 8, and Heloxy™ 61.

In an embodiment, the epoxide is3,4-epoxycyclohexylmethyl-3′,4-epoxycyclohexanecarboxylate (available asCELLOXIDE™ 2021P from Daicel Chemical, or as CYRACURE™ UVR-6105 from DowChemical), hydrogenated bisphenol A-epichlorohydrin based epoxy resin(available as EPON™ 1510 from Momentive), 1,4-cyclohexanedimethanoldiglycidyl ether (available as HELOXY™ 107 from Momentive), ahydrogenated bisphenol A diglycidyl ether (available as EPON™ 825 fromMomentive) a mixture of dicyclohexyl diepoxide and nanosilica (availableas NANOPDX™), and any combination thereof.

The above-mentioned cationically polymerizable compounds can be usedsingly or in combination of two or more thereof. In embodiments of theinvention, the cationic polymerizable component further comprises atleast two different epoxy components. In a specific embodiment, thecationic polymerizable component includes a cycloaliphatic epoxy, forexample, a cycloaliphatic epoxy with 2 or more than 2 epoxy groups. Inanother specific embodiment, the cationic polymerizable componentincludes an epoxy having an aromatic or aliphatic glycidyl ether groupwith 2 (difunctional) or more than 2 (polyfunctional) epoxy groups.

The liquid radiation curable resin for additive fabrication cantherefore include suitable amounts of the cationic polymerizablecomponent, for example, in certain embodiments, in an amount from about10 to about 80% by weight of the resin composition, in furtherembodiments from about 20 to about 70 wt % of the resin composition, andin further embodiments from about 25 to about 65 wt % of the resincomposition.

In other embodiments of the invention, the cationic polymerizablecomponent also optionally comprises an oxetane component. In a specificembodiment, the cationic polymerizable component includes an oxetane,for example, an oxetane containing 1, 2 or more than 2 oxetane groups.If utilized in the composition, the oxetane component is present in asuitable amount from about 5 to about 30 wt % of the resin composition.In another embodiment, the oxetane component is present in an amountfrom about 10 to about 25 wt % of the resin composition, and in yetanother embodiment, the oxetane component is present in an amount from20 to about 30 wt % of the resin composition.

In accordance with an embodiment, the liquid radiation curable resincomposition for additive fabrication contains a component that ispolymerizable by both free-radical polymerization and cationicpolymerization. An example of such a polymerizable component is avinyloxy compound, for example, one selected from the group consistingof bis(4-vinyloxybutyl)isophthalate, tris(4-vinyloxybutyl) trimellitate,and combinations thereof. Other examples of such a polymerizablecomponent include those containing an acrylate and an epoxy group, or anacrylate and an oxetane group, on a same molecule.

Radically Polymerizable Component

In accordance with an embodiment of the invention, the liquid radiationcurable resin for additive fabrication of the invention comprises atleast one free-radical polymerizable component, that is, a componentwhich undergoes polymerization initiated by free radicals. Thefree-radical polymerizable components are monomers, oligomers, and/orpolymers; they are monofunctional or polyfunctional materials, i.e.,have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 . . . 20 . . . 30 . . . 40 . . . 50 .. . 100, or more functional groups that can polymerize by free radicalinitiation, may contain aliphatic, aromatic, cycloaliphatic,arylaliphatic, heterocyclic moiety(ies), or any combination thereof.Examples of polyfunctional materials include dendritic polymers such asdendrimers, linear dendritic polymers, dendrigraft polymers,hyperbranched polymers, star branched polymers, and hypergraft polymers;see, e.g., US 2009/0093564 A1. The dendritic polymers may contain onetype of polymerizable functional group or different types ofpolymerizable functional groups, for example, acrylates and methacrylatefunctions.

Examples of free-radical polymerizable components include acrylates andmethacrylates such as isobornyl (meth)acrylate, bornyl (meth)acrylate,tricyclodecanyl (meth)acrylate, dicyclopentanyl (meth)acrylate,dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloyl morpholine,(meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate,ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate,butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate,t-butyl (meth)acrylate, pentyl (meth)acrylate, caprolactone acrylate,isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate,octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl(meth)acrylate, tridecyl (meth)acrylate, undecyl (meth)acrylate, lauryl(meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate,tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate,ethoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate,phenoxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate,polypropylene glycol mono(meth)acrylate, methoxyethylene glycol(meth)acrylate, ethoxyethyl (meth)acrylate, methoxypolyethylene glycol(meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone(meth)acrylamide, beta-carboxyethyl (meth)acrylate, phthalic acid(meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl(meth)acrylate, butylcarbamylethyl (meth)acrylate, n-isopropyl(meth)acrylamide fluorinated (meth)acrylate, 7-amino-3,7-dimethyloctyl(meth)acrylate.

Examples of polyfunctional free-radical polymerizable components includethose with (meth)acryloyl groups such as trimethylolpropanetri(meth)acrylate, pentaerythritol (meth)acrylate, ethylene glycoldi(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate,dicyclopentadiene dimethanol di(meth)acrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate;3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecanedi(meth)acrylate; dipentaerythritol monohydroxypenta(meth)acrylate,propoxylated trimethylolpropane tri(meth)acrylate, propoxylatedneopentyl glycol di(meth)acrylate, tetraethylene glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, polybutanediol di(meth)acrylate, tripropyleneglycoldi(meth)acrylate, glycerol tri(meth)acrylate, phosphoric acid mono- anddi(meth)acrylates, C₇-C₂₀ alkyl di(meth)acrylates,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)crylate, tricyclodecane diyl dimethyldi(meth)acrylate and alkoxylated versions (e.g., ethoxylated and/orpropoxylated) of any of the preceding monomers, and alsodi(meth)acrylate of a diol which is an ethylene oxide or propylene oxideadduct to bisphenol A, di(meth)acrylate of a diol which is an ethyleneoxide or propylene oxide adduct to hydrogenated bisphenol A, epoxy(meth)acrylate which is a (meth)acrylate adduct to bisphenol A ofdiglycidyl ether, diacrylate of polyoxyalkylated bisphenol A, andtriethylene glycol divinyl ether, and adducts of hydroxyethyl acrylate.

In accordance with an embodiment, the radically polymerizable componentis a polyfunctional (meth)acrylate. The polyfunctional (meth)acrylatesmay include all methacryloyl groups, all acryloyl groups, or anycombination of methacryloyl and acryloyl groups. In an embodiment, thefree-radical polymerizable component is selected from the groupconsisting of bisphenol A diglycidyl ether di(meth)acrylate, ethoxylatedor propoxylated bisphenol A or bisphenol F di(meth)acrylate,dicyclopentadiene dimethanol di(meth)acrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate, dipentaerythritol monohydroxypenta(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)crylate, propoxylated trimethylolpropane tri(meth)acrylate,and propoxylated neopentyl glycol di(meth)acrylate, and any combinationthereof.

In a preferred embodiment, the polyfunctional (meth)acrylate has morethan 2, more preferably more than 3, and more preferably greater than 4functional groups.

In another preferred embodiment, the radically polymerizable componentconsists exclusively of a single polyfunctional (meth)acrylatecomponent. In further embodiments, the exclusive radically polymerizablecomponent is tetra-functional, in further embodiments, the exclusiveradically polymerizable component is penta-functional, and in furtherembodiments, the exclusive radically polymerizable component ishexa-functional.

In another embodiment, the free-radical polymerizable component isselected from the group consisting of bisphenol A diglycidyl etherdiacrylate, dicyclopentadiene dimethanol diacrylate,[2-[1,1-dimethyl-2-[(1-oxoallyl)oxy]ethyl]-5-ethyl-1,3-dioxan-5-yl]methylacrylate, dipentaerythritol monohydroxypentaacrylate, propoxylatedtrimethylolpropane triacrylate, and propoxylated neopentyl glycoldiacrylate, and any combination thereof.

In specific embodiments, the liquid radiation curable resins foradditive fabrication of the invention include one or more of bisphenol Adiglycidyl ether di(meth)acrylate, dicyclopentadiene dimethanoldi(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate,propoxylated trimethylolpropane tri(meth)acrylate, and/or propoxylatedneopentyl glycol di(meth)acrylate, and more specifically one or more ofbisphenol A diglycidyl ether diacrylate, dicyclopentadiene dimethanoldiacrylate, dipentaerythritol pentaacrylate, propoxylatedtrimethylolpropane triacrylate, and/or propoxylated neopentyl glycoldiacrylate.

The above-mentioned radically polymerizable compounds can be used singlyor in combination of two or more thereof. The liquid radiation curableresin for additive fabrication can include any suitable amount of thefree-radical polymerizable components, for example, in certainembodiments, in an amount up to about 40 wt % of the resin composition,in certain embodiments, from about 2 to about 40 wt % of the resincomposition, in other embodiments from about 5 to about 30 wt %, and infurther embodiments from about 10 to about 20 wt % of the resincomposition.

Hydroxy Functional Components

Many of the known liquid radiation curable resin compositions foradditive fabrication use hydroxy-functional compounds to enhance theproperties of the parts made from the resin compositions.

In certain embodiments of the invention, the resin composition mayoptionally contain a hydroxy-functional component. Thehydroxyl-containing material which can be used in the present inventionmay be any suitable organic material having a hydroxyl functionality ofat least 1. If present, the material is preferably substantially free ofany groups which interfere with the curing reactions or which arethermally or photolytically unstable.

If present, any hydroxy group may be employed for the particularpurpose. If present, the hydroxyl-containing material preferablycontains one or more primary or secondary aliphatic hydroxyl. Thehydroxyl group may be internal in the molecule or terminal. Monomers,oligomers or polymers can be used. The hydroxyl equivalent weight, i.e.,the number average molecular weight divided by the number of hydroxylgroups, is preferably in the range of 31 to 5000.

Representative examples of hydroxyl-containing materials having ahydroxyl functionality of 1 include alkanols, monoalkyl ethers ofpolyoxyalkyleneglycols, mohoalkyl ethers of alkyleneglycols, and others,and combinations thereof.

Representative examples of monomeric polyhydroxy organic materialsinclude alkylene and arylalkylene glycols and polyols, such as1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,3-heptanetriol,2,6-dimethyl-1,2,6-hexanetriol,(2R,3R)-(−)-2-benzyloxy-1,3,4-butanetriol, 1,2,3-hexanetriol,1,2,3-butanetriol, 3-methyl-1,3,5-pentanetriol, 1,2,3-cyclohexanetriol,1,3,5-cyclohexanetriol, 3,7,11,15-tetramethyl-1,2,3-hexadecanetriol,2-hydroxymethyltetrahydropyran-3,4,5-triol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,3-cyclopentanediol,trans-1,2-cyclooctanediol, 1,16-hexadecanediol,3,6-dithia-1,8-octanediol, 2-butyne-1,4-diol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1-phenyl-1,2-ethanediol,1,2-cyclohexanediol, 1,5-decalindiol, 2,5-dimethyl-3-hexyne-2,5-diol,2,7-dimethyl-3,5-octadiyne-2-7-diol, 2,3-butanediol,1,4-cyclohexanedimethanol, and combinations thereof.

Representative examples of oligomeric and polymeric hydroxyl-containingmaterials include polyoxyethylene and polyoxypropylene glycols andtriols of molecular weights from about 200 to about 10,000;polytetramethylene glycols of varying molecular weight;poly(oxyethylene-oxybutylene) random or block copolymers; copolymerscontaining pendant hydroxy groups formed by hydrolysis or partialhydrolysis of vinyl acetate copolymers, polyvinylacetal resinscontaining pendant hydroxyl groups; hydroxy-terminated polyesters andhydroxy-terminated polylactones; hydroxy-functionalized polyalkadienes,such as polybutadiene; aliphatic polycarbonate polyols, such as analiphatic polycarbonate diol; and hydroxy-terminated polyethers, andcombinations thereof.

If present, preferred hydroxyl-containing monomers include1,4-cyclohexanedimethanol and aliphatic and cycloaliphatic monohydroxyalkanols. Such preferred hydroxyl-containing oligomers and polymersinclude hydroxyl and hydroxyl/epoxy functionalized polybutadiene,polycaprolactone diols and triols, ethylene/butylene polyols, andmonohydroxyl functional monomers. Preferred examples of polyetherpolyols are polypropylene glycols of various molecular weights andglycerol propoxylate-B-ethoxylate triol. If present, especiallypreferred are linear and branched polytetrahydrofuran polyether polyolsavailable in various molecular weights, such as in the range of 150-4000g/mol, preferably in the range of 150-1500 g/mol, more preferably in therange of 150-750 g/mol.

If present, the resin composition preferably comprises, relative to thetotal weight of the resin composition, at most 10 wt % of one or morenon-free radical polymerizable hydroxy-functional compounds, morepreferably at most 5 wt %, and most preferably at most 2 wt %.

In embodiments, the liquid radiation curable resin for additivefabrication of the present invention includes a photoinitiating system.The photoinitiating system can include a free-radical photoinitiatorand/or a cationic photoinitiator. In accordance with an embodiment, theliquid radiation curable resin composition includes a photoinitiatingsystem contains at least one photoinitiator having a cationic initiatingfunction, and at least one photoinitiator having a free radicalinitiating function. Additionally, the photoinitiating system caninclude a photoinitiator that contains both free-radical initiatingfunction and cationic initiating function on the same molecule. Thephotoinitiator is a compound that chemically changes due to the actionof light or the synergy between the action of light and the electronicexcitation of a sensitizing dye to produce at least one of a radical, anacid, and a base.

Cationic Photoinitiator

In accordance with an embodiment, the liquid radiation curable resincomposition includes a cationic photoinitiator. The cationicphotoinitiator initiates cationic ring-opening polymerization uponirradiation of light.

In an embodiment, any suitable cationic photoinitiator can be used, forexample, those with cations selected from the group consisting of oniumsalts, halonium salts, iodosyl salts, selenium salts, sulfonium salts,sulfoxonium salts, diazonium salts, metallocene salts, isoquinoliniumsalts, phosphonium salts, arsonium salts, tropylium salts,dialkylphenacylsulfonium salts, thiopyrilium salts, diaryl iodoniumsalts, triaryl sulfonium salts, ferrocenes,di(cyclopentadienyliron)arene salt compounds, and pyridinium salts, andany combination thereof.

In another embodiment, the cation of the cationic photoinitiator isselected from the group consisting of aromatic diazonium salts, aromaticsulfonium salts, aromatic iodonium salts, metallocene based compounds,aromatic phosphonium salts, and any combination thereof. In anotherembodiment, the cation is a polymeric sulfonium salt, such as in U.S.Pat. No. 5,380,923 or U.S. Pat. No. 5,047,568, or other aromaticheteroatom-containing cations and naphthyl-sulfonium salts such as inU.S. Pat. No. 7,611,817, U.S. Pat. No. 7,230,122, US2011/0039205,US2009/0182172, U.S. Pat. No. 7,678,528, EP2308865, WO2010046240, orEP2218715. In another embodiment, the cationic photoinitiator isselected from the group consisting of triarylsulfonium salts,diaryliodonium salts, and metallocene based compounds, and anycombination thereof. Onium salts, e.g., iodonium salts and sulfoniumsalts, and ferrocenium salts, have the advantage that they are generallymore thermally stable.

In a particular embodiment, the cationic photoinitiator has an anionselected from the group consisting of BF₄ ⁻, AsF₆ ⁻, SbF₆ ⁻, PF₆ ⁻.[B(CF₃)₄]⁻, B(C₆F₅)₄ ⁻, B[C₆H₃-3,5(CF₃)₂]₄ ⁻, B(C₆H₄CF₃)₄ ⁻, B(C₆H₃F₂)₄⁻, B[C₆F₄-4(CF₃)]₄ ⁻, Ga(C₆F₅)₄ ⁻, [(C₆F₅)₃B—C₃H₃N₂—B(C₆F₅)₃]⁻,[(C₆F₅)₃B—NH₂—B(C₆F₅)₃]⁻, tetrakis(3,5-difluoro-4-alkyloxyphenyl)borate,tetrakis(2,3,5,6-tetrafluoro-4-alkyloxyphenyl)borate,perfluoroalkylsulfonates, tris[(perfluoroalkyl)sulfonyl]methides,bis[(perfluoroalkyl)sulfonyl]imides, perfluoroalkylphosphates,tris(perfluoroalkyl)trifluorophosphates,bis(perfluoroalkyl)tetrafluorophosphates,tris(pentafluoroethyl)trifluorophosphates, and (CH₆B₁₁Br₆)⁻,(CH₆B₁₁Cl₆)⁻ and other halogenated carborane anions.

A survey of other onium salt initiators and/or metallocene salts can befound in “UV Curing, Science and Technology”, (Editor S. P. Pappas,Technology Marketing Corp., 642 Westover Road, Stamford, Conn., U.S.A.)or “Chemistry & Technology of UV & EB Formulation for Coatings, Inks &Paints”, Vol. 3 (edited by P. K. T. Oldring).

In an embodiment, the cationic photoinitiator has a cation selected fromthe group consisting of aromatic sulfonium salts, aromatic iodoniumsalts, and metallocene based compounds with at least an anion selectedfrom the group consisting of SbF₆ ⁻, PF₆ ⁻, B(C₆F₅)₄ ⁻, [B(CF₃)₄]⁻,tetrakis(3,5-difluoro-4-methoxyphenyl)borate, perfluoroalkylsulfonates,perfluoroalkylphosphates, tris[(perfluoroalkyl)sulfonyl]methides, and[(C₂F₅)₃PF₃]⁻.

Examples of cationic photoinitiators useful for curing at 300-475 nm,particularly at 365 nm UV light, without a sensitizer include4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumhexafluoroantimonate,4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumtetrakis(pentafluorophenyl)borate,4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumtetrakis(3,5-difluoro-4-methyloxyphenyl)borate,4-[4-(3-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumtetrakis(2,3,5,6-tetrafluoro-4-methyloxyphenyl)borate,tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate (Irgacure® PAG 290 from BASF),tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtris[(trifluoromethyl)sulfonyl]methide (Irgacure® GSID 26-1 from BASF),tris(4-(4-acetylphenyl)thiophenyl)sulfonium hexafluorophosphate(Irgacure® 270 from BASF), and HS-1 available from San-Apro Ltd.

Preferred cationic photoinitiators include, either alone or in amixture: bis[4-diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate;thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure1176 from Chitec), tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate (Irgacure® PAG 290 from BASF),tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtris[(trifluoromethyl)sulfonyl]methide (Irgacure® GSID 26-1 from BASF),and tris(4-(4-acetylphenyl)thiophenyl)sulfonium hexafluorophosphate(Irgacure® 270 from BASF), [4-(1-methylethyl)phenyl](4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074from Rhodia),4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumhexafluoroantimonate (as SP-172 from Adeka), SP-300 from Adeka, andaromatic sulfonium salts with anions of (PF_(6-m)(C_(n)F_(2n+1))_(m))⁻where m is an integer from 1 to 5, and n is an integer from 1 to 4(available as CPI-200K or CPI-200S, which are monovalent sulfonium saltsfrom San-Apro Ltd., TK-1 available from San-Apro Ltd., or HS-1 availablefrom San-Apro Ltd.).

In various embodiments, the liquid radiation curable resin compositionfor additive fabrication may be irradiated by laser or LED lightoperating at any wavelength in either the UV or visible light spectrum.In particular embodiments, the irradiation is from a laser or LEDemitting a wavelength of from 340 nm to 415 nm. In particularembodiments, the laser or LED source emits a peak wavelength of about340 nm, 355 nm, 365 nm, 375 nm, 385 nm, 395 nm, 405 nm, or 415 nm.

In an embodiment of the invention, the liquid radiation curable resinfor additive fabrication comprises an aromatic triaryl sulfonium saltcationic photoinitiator.

Use of aromatic triaryl sulfonium salts in additive fabricationapplications is known. Please see US 20120251841 to DSM IP Assets, B.V.(which is hereby incorporated in its entirety), U.S. Pat. No. 6,368,769,to Asahi Denki Kogyo, which discusses aromatic triaryl sulfonium saltswith tetraryl borate anions, includingtetrakis(pentafluorophenyl)borate, and use of the compounds instereolithography applications. Triarylsulfonium salts are disclosed in,for example, J Photopolymer Science & Tech (2000), 13(1), 117-118 and JPoly Science, Part A (2008), 46(11), 3820-29. Triarylsulfonium saltsAr₃S⁺Mxn⁻ with complex metal halide anions such as BF₄ ⁻, AsF₆ ⁻, PF₆ ⁻,and SbF₆ ⁻, are disclosed in J Polymr Sci, Part A (1996), 34(16),3231-3253.

The use of aromatic triaryl sulfonium salts as the cationicphotoinitiator in liquid radiation curable resins is desirable inadditive fabrication processes because the resulting resin attains afast photospeed, good thermal-stability, and good photo-stability.

In a preferred embodiment, the cationic photoinitiator is an aromatictriaryl sulfonium salt that is more specifically an R-substitutedaromatic thioether triaryl sulfonium tetrakis(pentafluorophenyl)boratecationic photoinitiator, having a tetrakis(pentafluorophenyl)borateanion and a cation of the following formula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.

In an embodiment, Y1, Y2, and Y3 are the same. In another embodiment, Y1and Y2 are the same, but Y3 is different. In another embodiment, Y1, Y2,or Y3 are an R-substituted aromatic thioether with R being an acetyl orhalogen group. Preferably Y1, Y2, or Y3 are a para-R-substitutedaromatic thioether with R being an acetyl or halogen group.

A particularly preferred R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate cationic photoinitiator istris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate.Tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate is known commercially as IRGACURE®PAG-290 (formerly known by the development code GSID4480-1) and isavailable from Ciba/BASF.

An R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator, for instance,tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate, is also more thermally-stable thansome other cationic photoinitiators. The improved thermal-stabilityallows liquid radiation curable resins for additive fabricationincorporating a triaryl sulfonium tetrakis(pentafluorophenyl)boratecationic photoinitiator instead of other conventional cationicphotoinitiators to retain their viscosity at elevated temperatures forlong periods of time.

In another embodiment, the cationic photoinitiator is an aromatictriaryl sulfonium salt that possesses an anion represented by SbF₆ ⁻,PF₆ ⁻, BF₄ ⁻, (CF₃CF₂)₃PF₃ ⁻(C₆F₅)₄B⁻, ((CF₃)₂C₆H₃)₄B⁻, (C₆F₅)₄Ga⁻,((CF₃)₂C₆H₃)₄Ga⁻, trifluoromethanesulfonate, nonafluorobutanesulfonate,methanesulfonate, butanesulfonate, benzenesulfonate, orp-toluenesulfonate, and a cation of the following formula (II):

wherein in formula (II), R¹, R², R³, R⁵ and R⁶ each independentlyrepresent an alkyl group, a hydroxy group, an alkoxy group, analkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, anaryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group, anarylthio group, an alkylthio group, an aryl group, a heterocyclichydrocarbon group, an aryloxy group, an alkylsulfinyl group, anarylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, ahydroxy(poly)alkyleneoxy group, an optionally substituted amino group, acyano group, a nitro group, or a halogen atom, R⁴ represents an alkylgroup, a hydroxy group, an alkoxy group, an alkylcarbonyl group, analkoxycarbonyl group, an acyloxy group, an alkylthio group, aheterocyclic hydrocarbon group, an alkylsulfinyl group, an alkylsulfonylgroup, a hydroxy(poly)alkyleneoxy group, an optionally substituted aminogroup, a cyano group, a nitro group, or a halogen atom, m¹ to m⁶ eachrepresent the number of occurrences of each of R¹ to R⁶, m¹, m⁴, and m⁶each represent an integer of 0 to 5, m², m³, and m⁵ each represent aninteger of 0 to 4. Such photoinitiators are described in, for example,U.S. Pat. No. 8,617,787.

A particularly preferred aromatic triaryl sulfonium cationicphotoinitiator has an anion that is a fluoroalkyl-substitutedfluorophosphate. Commercial examples of an aromatic triaryl sulfoniumcationic photoinitiator having a fluoroalkyl-substituted fluorophosphateanion is the CPI-200 series (for example CPI-200K® or CPI-2105®) or 300series, available from San-Apro Limited.

In accordance with embodiments of the invention, the liquid radiationcurable resin for additive fabrication includes a cationic polymerizablecomponent in addition to an R-substituted aromatic thioether triarylsulfonium tetrakis(pentafluorophenyl)borate or fluoroalkyl-substitutedfluorophosphate cationic photoinitiator. In other embodiments, theliquid radiation curable resins for additive fabrication includecationic polymerizable components, free-radical photoinitiators, andfree-radical polymerizable components. In some embodiments, the liquidradiation curable resins for additive fabrication include anR-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl)borate cationic photoinitiator and additionalcationic photoinitiators and/or photosensitizers, along with a cationicpolymerizable component and, optionally, free-radical polymerizablecomponents and free-radical photoinitiators.

The liquid radiation curable resin composition can include any suitableamount of the cationic photoinitiator, for example, in certainembodiments, in an amount up to about 15% by weight of the resincomposition, in certain embodiments, up to about 5% by weight of theresin composition, and in further embodiments from about 2% to about 10%by weight of the resin composition, and in other embodiments, from about0.1% to about 5% by weight of the resin composition. In a furtherembodiment, the amount of cationic photoinitiator is from about 0.2 wt %to about 4 wt % of the total resin composition, and in other embodimentsfrom about 0.5 wt % to about 3 wt %.

In some embodiments, depending on the wavelength of light used forcuring the liquid radiation curable resin, it is desirable for theliquid radiation curable resin composition to include a photosensitizer.The term “photosensitizer” is used to refer to any substance that eitherincreases the rate of photoinitiated polymerization or shifts thewavelength at which polymerization occurs; see textbook by G. Odian,Principles of Polymerization, 3^(rd) Ed., 1991, page 222. A variety ofcompounds can be used as photosensitizers, including heterocyclic andfused-ring aromatic hydrocarbons, organic dyes, and aromatic ketones.Examples of photosensitizers include those selected from the groupconsisting of methanones, xanthenones, pyrenemethanols, anthracenes,pyrene, perylene, quinones, xanthones, thioxanthones, benzoyl esters,benzophenones, and any combination thereof. Particular examples ofphotosensitizers include those selected from the group consisting of[4-[(4-methylphenyl)thio]phenyl]phenyl-methanone,isopropyl-9H-thioxanthen-9-one, 1-pyrenemethanol,9-(hydroxymethyl)anthracene, 9,10-diethoxyanthracene,9,10-dimethoxyanthracene, 9,10-dipropoxyanthracene,9,10-dibutyloxyanthracene, 9-anthracenemethanol acetate,2-ethyl-9,10-dimethoxyanthracene, 2-methyl-9,10-dimethoxyanthracene,2-t-butyl-9,10-dimethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene and2-methyl-9,10-diethoxyanthracene, anthracene, anthraquinones,2-methylanthraquinone, 2-ethylanthraquinone, 2-tertbutylanthraquinone,1-chloroanthraquinone, 2-amylanthraquinone, thioxanthones and xanthones,isopropyl thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone,1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF fromBASF), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),4-benzoyl-4′-methyl diphenyl sulphide (Chivacure BMS from Chitec),4,4′-bis(diethylamino) benzophenone (Chivacure EMK from Chitec), and anycombination thereof.

The novel mixtures may also contain various photoinitiators of differentsensitivity to radiation of emission lines with different wavelengths toobtain a better utilization of a UV light source. The use of knownphotoinitiators of different sensitivity to radiation of emission linesis well known in the art of additive fabrication, and may be selected inaccordance with radiation sources of, for example, 351, nm 355 nm, 365nm, 385 nm, and 405 nm. In this context it is advantageous for thevarious photoinitiators to be selected such, and employed in aconcentration such, that equal optical absorption is produced with theemission lines used.

The liquid radiation curable resin composition for additive fabricationcan include any suitable amount of the photosensitizer, for example, incertain embodiments, in an amount up to about 10% by weight of the resincomposition, in certain embodiments, up to about 5% by weight of theresin composition, and in further embodiments from about 0.05% to about2% by weight of the resin composition.

Other Cationic Photoinitiators and Photosensitizers

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes a cationic photoinitiator in addition to,or in lieu of, an R-substituted aromatic thioether triaryl sulfoniumtetrakis(pentafluorophenyl) borate cationic photoinitiator. Any suitablecationic photoinitiator can be used, for example, those selected fromthe group consisting of onium salts, halonium salts, iodosyl salts,selenium salts, sulfonium salts, sulfoxonium salts, diazonium salts,metallocene salts, isoquinolinium salts, phosphonium salts, arsoniumsalts, tropylium salts, dialkylphenacylsulfonium salts, thiopyriliumsalts, diaryl iodonium salts, triaryl sulfonium salts, sulfoniumantimonate salts, ferrocenes, di(cyclopentadienyliron)arene saltcompounds, and pyridinium salts, and any combination thereof. Oniumsalts, e.g., iodonium salts, sulfonium salts and ferrocenes, have theadvantage that they are thermally-stable.

Preferred mixtures of cationic photoinitiators include a mixture of:bis[4-diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate;thiophenoxyphenylsulfonium hexafluoroantimonate (available as Chivacure1176 from Chitec); tris(4-(4-acetylphenyl)thiophenyl)sulfoniumtetrakis(pentafluorophenyl)borate (Irgacure PAG-290 or GSID4480-1 fromCiba/BASF), iodonium, [4-(1-methylethyl)phenyl](4-methylphenyl)-,tetrakis(pentafluorophenyl)borate (available as Rhodorsil 2074 fromRhodia),4-[4-(2-chlorobenzoyl)phenylthio]phenylbis(4-fluorophenyl)sulfoniumhexafluoroantimonate (as SP-172) and SP-300 (both available from Adeka).

Additionally, photosensitizers are useful in combination withphotoinitiators in effecting cure with LED light sources emitting in thewavelength range of 300-475 nm. Examples of suitable photosensitizersinclude: anthraquinones, such as 2-methylanthraquinone,2-ethylanthraquinone, 2-tertbutylanthraquinone, 1-chloroanthraquinone,and 2-amylanthraquinone, thioxanthones and xanthones, such as isopropylthioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF fromCiba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),4-benzoyl-4′-methyl diphenyl sulphide (Chivacure BMS from Chitec),4,4′-bis(diethylamino) benzophenone (Chivacure EMK from Chitec).

In an embodiment, the photosensitizer is a fluorone, e.g.,5,7-diiodo-3-butoxy-6-fluorone, 5,7-diiodo-3-hydroxy-6-fluorone,9-cyano-5,7-diiodo-3-hydroxy-6-fluorone, or a photosensitizer is

and any combination thereof.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the photosensitizer, for example, in certainembodiments, in an amount up to about 10% by weight of the resincomposition, in certain embodiments, up to about 5% by weight of theresin composition, and in further embodiments from about 0.05% to about2% by weight of the resin composition.

When photosensitizers are employed, other photoinitiators absorbing atshorter wavelengths can be used. Examples of such photoinitiatorsinclude: benzophenones, such as benzophenone, 4-methyl benzophenone,2,4,6-trimethyl benzophenone, and dimethoxybenzophenone, and1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone,phenyl (1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hydroxyethoxyl)phenyl]-2-methyl-1-propanone, and4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal, andoligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (EsacureKIP 150 from Lamberti).

A photosensitizer or co-initiator may be used to improve the activity ofthe cationic photoinitiator. It is for either increasing the rate ofphotoinitiated polymerization or shifting the wavelength at whichpolymerization occurs. The sensitizer used in combination with theabove-mentioned cationic photoinitiator is not particularly limited. Avariety of compounds can be used as photosensitizers, includingheterocyclic and fused-ring aromatic hydrocarbons, organic dyes, andaromatic ketones. Examples of sensitizers include compounds disclosed byJ. V. Crivello in Advances in Polymer Science, 62, 1 (1984), and by J.V. Crivello & K. Dietliker, “Photoinitiators for CationicPolymerization” in Chemistry & technology of UV & EB formulation forcoatings, inks & paints. Volume III, Photoinitiators for free radicaland cationic polymerization. by K. Dietliker; [Ed. by P. K. T. Oldring],SITA Technology Ltd, London, 1991. Specific examples includepolyaromatic hydrocarbons and their derivatives such as anthracene,pyrene, perylene and their derivatives, thioxanthones,α-hydroxyalkylphenones, 4-benzoyl-4′-methyldiphenyl sulfide, acridineorange, and benzoflavin.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the other cationic photoinitiator orphotosensitizer, for example, in certain embodiments, in an amount anamount from 0.1 to 10 wt % of the resin composition, in certainembodiments, from about 1 to about 8 wt % of the resin composition, andin further embodiments from about 2 to about 6 wt % of the resincomposition. In an embodiment, the above ranges are particularlysuitable for use with epoxy monomers.

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes a photoinitiating system that is aphotoinitiator having both cationic initiating function and free radicalinitiating function.

Free-Radical Photoinitiator

Typically, free radical photoinitiators are divided into those that formradicals by cleavage, known as “Norrish Type I” and those that formradicals by hydrogen abstraction, known as “Norrish type II”. TheNorrish type II photoinitiators require a hydrogen donor, which servesas the free radical source. As the initiation is based on a bimolecularreaction, the Norrrish type II photoinitiators are generally slower thanNorrish type I photoinitiators which are based on the unimolecularformation of radicals. On the other hand, Norrish type IIphotoinitiators possess better optical absorption properties in thenear-UV spectroscopic region. Photolysis of aromatic ketones, such asbenzophenone, thioxanthones, benzil, and quinones, in the presence ofhydrogen donors, such as alcohols, amines, or thiols leads to theformation of a radical produced from the carbonyl compound (ketyl-typeradical) and another radical derived from the hydrogen donor. Thephotopolymerization of vinyl monomers is usually initiated by theradicals produced from the hydrogen donor. The ketyl radicals areusually not reactive toward vinyl monomers because of the sterichindrance and the delocalization of an unpaired electron.

To successfully formulate a liquid radiation curable resin for additivefabrication, it is necessary to review the wavelength sensitivity of thephotoinitiator(s) present in the resin composition to determine if theywill be activated by the radiation source chosen to provide the curinglight.

In accordance with an embodiment, the liquid radiation curable resin foradditive fabrication includes at least one free radical photoinitiator,e.g., those selected from the group consisting of benzoylphosphineoxides, aryl ketones, benzophenones, hydroxylated ketones,1-hydroxyphenyl ketones, ketals, metallocenes, and any combinationthereof.

In an embodiment, the liquid radiation curable resin for additivefabrication includes at least one free-radical photoinitiator selectedfrom the group consisting of 2,4,6-trimethylbenzoyl diphenylphosphineoxide and 2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone,2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one,4-benzoyl-4′-methyl diphenyl sulphide, 4,4′-bis(diethylamino)benzophenone, and 4,4′-bis(N,N′-dimethylamino) benzophenone (Michler'sketone), benzophenone, 4-methyl benzophenone, 2,4,6-trimethylbenzophenone, dimethoxybenzophenone, 1-hydroxycyclohexyl phenyl ketone,phenyl (1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hydroxyethoxyl)phenyl]-2-methyl-1-propanone,4-isopropylphenyl(1-hydroxyisopropyl)ketone,oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone],camphorquinone, 4,4′-bis(diethylamino) benzophenone, benzil dimethylketal, bis(eta 5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium, and any combinationthereof.

For light sources emitting in the 300-475 nm wavelength range,especially those emitting at 365 nm, 390 nm, or 395 nm, examples ofsuitable free-radical photoinitiators absorbing in this area include:benzoylphosphine oxides, such as, for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO from BASF) and2,4,6-trimethylbenzoyl phenyl, ethoxy phosphine oxide (Lucirin TPO-Lfrom BASF), bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (Irgacure819 or BAPO from Ciba),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (Irgacure 907from Ciba),2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone(Irgacure 369 from Ciba),2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one(Irgacure 379 from Ciba), 4-benzoyl-4′-methyl diphenyl sulphide(Chivacure BMS from Chitec), 4,4′-bis(diethylamino) benzophenone(Chivacure EMK from Chitec), and 4,4′-bis(N,N′-dimethylamino)benzophenone (Michler's ketone). Also suitable are mixtures thereof.

Additionally, photosensitizers are useful in conjunction withphotoinitiators in effecting cure with LED light sources emitting inthis wavelength range. Examples of suitable photosensitizers include:anthraquinones, such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tertbutylanthraquinone, 1-chloroanthraquinone, and2-amylanthraquinone, thioxanthones and xanthones, such as isopropylthioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, and1-chloro-4-propoxythioxanthone, methyl benzoyl formate (Darocur MBF fromCiba), methyl-2-benzoyl benzoate (Chivacure OMB from Chitec),4-benzoyl-4′-methyl diphenyl sulphide (Chivacure BMS from Chitec),4,4′-bis(diethylamino) benzophenone (Chivacure EMK from Chitec).

It is possible for UV radiation sources to be designed to emit light atshorter wavelengths. For light sources emitting at wavelengths frombetween about 100 and about 300 nm, it is possible to employ aphotosensitizer with a photoinitiator. When photosensitizers, such asthose previously listed are present in the formulation, otherphotoinitiators absorbing at shorter wavelengths can be used. Examplesof such photoinitiators include: benzophenones, such as benzophenone,4-methyl benzophenone, 2,4,6-trimethyl benzophenone,dimethoxybenzophenone, and 1-hydroxyphenyl ketones, such as1-hydroxycyclohexyl phenyl ketone, phenyl (1-hydroxyisopropyl)ketone,2-hydroxy-1-[4-(2-hroxyethoxy)phenyl]-2-methyl-1-propanone, and4-isopropylphenyl(1-hydroxyisopropyl)ketone, benzil dimethyl ketal, andoligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone] (EsacureKIP 150 from Lamberti).

Radiation sources can also be designed to emit at higher wavelengths.For radiation sources emitting light at wavelengths from about 475 nm toabout 900 nm, examples of suitable free radical photoinitiators include:camphorquinone, 4,4′-bis(diethylamino) benzophenone (Chivacure EMK fromChitec), 4,4′-bis(N,N′-dimethylamino) benzophenone (Michler's ketone),bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (“BAPO,” or Irgacure819 from Ciba), metallocenes such as bis (eta 5-2-4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium (Irgacure 784 fromCiba), and the visible light photoinitiators from Spectra Group Limited,Inc. such as H-Nu 470, H-Nu-535, H-Nu-635, H-Nu-Blue-640, andH-Nu-Blue-660.

In one embodiment of the instant claimed invention, the light emitted bythe radiation source is UVA radiation, which is radiation with awavelength between about 320 and about 400 nm. In one embodiment of theinstant claimed invention, the light emitted by the radiation source isUVB radiation, which is radiation with a wavelength between about 280and about 320 nm. In one embodiment of the instant claimed invention,the light emitted by the radiation source is UVC radiation, which isradiation with a wavelength between about 100 and about 280 nm.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of the free-radical photoinitiator as component (d),for example, in certain embodiments, in an amount up to about 10 wt % ofthe resin composition, in certain embodiments, from about 0.1 to about10 wt % of the resin composition, and in further embodiments from about1 to about 6 wt % of the resin composition.

Fillers

The liquid radiation curable composition for additive fabricationaccording to the present invention also comprises at least one filler.Inorganic substances are especially preferred as fillers because oftheir tendency to impart water-resistance, heat-resistance, and robustmechanical properties into the cured, solid three-dimensional parts madetherefrom.

In an embodiment, a filler of which the particles are spherical—hereindefined as having a sphericity of 0.80 or greater—is used, because ofthe improved molding properties and accuracy they impart into threedimensional objects made of the prepared resin composition of thepresent invention.

Sphericity, also known as the “degree of circularity”, is a ratio thatmeasures the deviation of a spherical object from being a perfectsphere, and is defined by formula (III). When the shape of a projectedimage is exactly spherical, the sphericity is defined as 1. Sphericitymay be calculated by the following formula (III):

$\begin{matrix}{{Sphericity} = {\frac{\left. \sqrt{}4 \right.\; \pi \; S_{p}}{C} = \frac{d_{pa}}{d_{pc}}}} & ({III})\end{matrix}$

wherein S_(p) is a projection area, C is the peripheral length of theprojected image, d_(pa) is the diameter of a circle having the same areaas that of the projection area, and d_(pc) is the diameter of a circlehaving the same peripheral length as the projected image of theparticle.

This sphericity can be measured using an image analyzer which cananalyze a microphotograph taken by a scanning electron microscope (SEM).The average sphericity can be measured by calculating the averagesphericity of 100 particles arbitrarily selected from a multitude ofparticles appearing in the microphotograph.

In an embodiment of the invention, the filler is inorganic and comprisesceramics such as silica (SiO₂) nanoparticles, i.e., those particleshaving a mean particle size of from between 1 nanometer (nm) to 999 nm,or microparticles, i.e., those particles having a mean particle size ofbetween 1 micrometer (μm) to 999 μm. Average particle size may bemeasured using laser diffraction particle size analysis in accordancewith ISO13320:2009. A suitable device for measuring the average particlediameter of nanoparticles is the LB-550 machine, available from HoribaInstruments, Inc, which measures particle diameter by dynamic lightscattering.

The nanoparticles or microparticles may be substantially silica basedpowders, for instance, greater than 85 wt %, more preferably 90 wt %,more preferably 95 wt % of silica (SiO₂). Certain non-limiting examplesof commercially available silica powder products include Crystallite3K-S, Crystallite NX-7, Crystallite MCC-4, Crystallite CMC-12,Crystallite A-1, Crystallite AA, Crystallite C, Crystallite D,Crystallite CMC-1, Crystallite C-66, Crystallite 5X, Crystallite 2A-2,Crystallite VX-S2, Crystallite VX-SR, Crystallite VX-X, CrystalliteVX-S, HUSELEX RD-8, HUSELEX RD-120, HUSELEX MCF-4, HUSELEX GP-200T,HUSELEX ZA-30, HUSELEX RD-8, HUSELEX Y-40, HUSELEX E-2, HUSELEX Y-60,HUSELEX E-1, HUSELEX E-2, HUSELEX FF, HUSELEX X, HUSELEX ZA-20, IMSILA-25, IMSIL A-15, IMSIL A-10, and IMSIL A-8, (Ryushin Co., Ltd.);ORGANOSILICASOL™ MEK-EC-2102, ORGANOSILICASOL™ MEK-EC-2104,ORGANOSILICASOL™ MEK-AC-2202, ORGANOSILICASOL™ MEK-AC-4101,ORGANOSILICASOL™ MEK-AC-5101, ORGANOSILICASOL™ MIBK-SD, ORGANOSILICASOL™MIBK-SD-L, ORGANOSILICASOL™ DMAC-ST, ORGANOSILICASOL™ EG-ST,ORGANOSILICASOL™ IPA-ST, ORGANOSILICASOL™ IPA-ST-L, ORGANOSILICASOL™IPA-ST-L-UP, ORGANOSILICASOL™ IPA-ST-ZL, ORGANOSILICASOL™ MA-ST-M,ORGANOSILICASOL™ MEK-ST, ORGANOSILICASOL™ MEK-ST-L, ORGANOSILICASOL™MEK-ST-UP, ORGANOSILICASOL™ MIBK-ST, ORGANOSILICASOL™ MT-ST,ORGANOSILICASOL™ NPC-ST-30, ORGANOSILICASOL™ PMA-ST, SUNSPHERE H-31,SUNSPHERE H-32, SUNSPHERE H-51, SUNSPHERE H-52, SUNSPHERE H-121,SUNSPHERE H-122, SUNSPHERE L-31, SUNSPHERE L-51, SUNSPHERE L-121,SUNSPHERE NP-30, SUNSPHERE NP-100, and SUNSPHERE NP-200 (Asahi GlassCo., Ltd.); Silstar MK-08 and MK-15 (Nippon Chemical Industrial Co.,Ltd.); FB-48 (Denki Kagaku Kogyo K.K.); Nipsil SS-10, Nipsi:L SS-15,Nipsil SS-10A, Nipsil SS-20, Nipsil SS-30P, Nipsil SS-30S, Nipsil SS-40,Nipsil SS-50, Nipsil SS-50A, Nipsil SS-70, Nipsil SS-100, Nipsil SS-10F,Nipsil SS-50F, Nipsil SS-50B, Nipsil SS-50C, Nipsil SS-72F, NipsilSS-170X, Nipsil SS-178B, Nipsil E150K, Nipsil E-150J, Nipsil E-1030,Nipsil ST-4, Nipsil E-170, Nipsil E-200, Nipsil E-220, Nipsil E-200A,Nipsil E-1009, Nipsil E-220A, Nipsil E-1011, NipsilE-K300, Nipsil HD,Nipsil HD-2, Nipsil N-300A, Nipsil L-250, Nipsil G-300, Nipsil E-75,Nipsil E-743, and Nipsil E-74P (Nippon Silica Industry, Ltd.). Pleasesee U.S. Pat. No. 6,013,714 for further examples of silica particles.

In other embodiments of the invention, alternative inorganic fillersubstances may be used, such as those containing glass or metalparticles. Certain non-limiting examples of such substances include:glass powder, alumina, alumina hydrate, magnesium oxide, magnesiumhydroxide, barium sulfate, calcium sulfate, calcium carbonate, magnesiumcarbonate, silicate mineral, diatomaceous earth, silica sand, silicapowder, oxidation titanium, aluminum powder, bronze, zinc powder, copperpowder, lead powder, gold powder, silver dust, glass fiber, titanic acidpotassium whiskers, carbon whiskers, sapphire whiskers, verificationrear whiskers, boron carbide whiskers, silicon carbide whiskers, andsilicon nitride whiskers.

Certain non-limiting examples of such other commercially availableinorganic filler products include Glass bead GB210, GB210A, GB210B,GB210C, GB045Z, GB045ZA, GB045ZB, GB045ZC, GB731, GB731A, GB731B,GB731C, GB731M, GB301S, EGB210, EGB210A, EGB210B, EGB210C, EGB045Z,EGB045ZA, EGB045ZB, EGB045ZC, MB-10, MB-20, EMB-10, EMB-20, HSC070Q,HSC-024X, HSC-080S, HSC-070G, HSC-075L, HSC-110, HSC-110A, HSC-110B, andHSC-110C (Toshiba Balotini Co., Ltd.); Radiolite #100, Radiolite FineFlow B, Radiolite Fine Flow A, Radiolite Sparkle Flow, Radiolite SpecialFlow, Radiolite #300, Radiolite #200, Radiolite Clear Flow, Radiolite#500, Radiolite #600, Radiolite #2000, Radiolite #700, Radiolite #500S,Radiolite #800, Radiolite #900, Radiolite #800S, Radiolite #3000,Radiolite Ace, Radiolite Superace, Radiolite High Ace, Radiolite PC-1,Radiolite Delux P-5, Radiolite Delux W50, Radiolite Microfine, RadioliteF, Radic)lite SPF, Radiolite GC, Topco #31, Topco #34, Topco #36, Topco#38, and Topco #54 (Showa Chemical Industry Co., Ltd.); Higilite H-X,Higilite H-21, Higilite H-31, Higilite H-32, Higilite H-42, HigiliteH-42M, Higilite H-43, Higilite H-32ST, Higilite H-42STV, Higilite H-42T,Higilite H-34, Higilite H-34HL, Higilite H-32I, Higilite H-42I, HigiliteH-425, Higilite H-210, Higilite H-310, Higilite H-320, Higilite H-141,Higilite H-241, Higilite H-341, Higilite H-3201, Higilite H-320ST,Higilite HS-310, Higilite HS-320, Higilite HS-341, Alumina A-426,alumina A-42-1, Alumina A-42-2, Alumina A-42-3, Alumina A-420, AluminaA-43M, Alumina A-43-L, Alumina A-50-K, Alumina A-50-N, Alumina A-50-F,Alumina AL-45-H, Alumina AL-45-2, Alumina AL-45-1, Alumina AL-43-M,Alumina AL-43-L, Alumina AL-43PC, Alumina AL-150SG, Alumina AL-170,Alumina A-172, Alumina A-173, Alumina AS10, Alumina AS-20, AluminaAS-30, Alumina AS-40, and Alumina AS-50 (Showa Denko K.K.); Starmague U,Starmague M, Starmague L, Starmague P, Starmague C, Starmague CX, Highpurity magnesia HP-10, High purity magnesia HP-10N, High purity magnesiaHP-30, Star brand-200, Star brand-10, Star brand-10A, Star brandmagnesium carbonate Venus, Star brand magnesium carbonate two stars,Star brand magnesium carbonate one star, Star brand magnesium carbonateS, Star brand magnesium carbonate Fodder, Star brand heavy magnesiumcarbonate, High purity magnesium carbonate GP-10, High purity magnesiumcarbonate 30, Star brand light calcium carbonate general use, Star brandlight calcium carbonates EC, and Star brand light calcium carbonateKFW-200 (Konoshima Chemical Industry Co., Ltd.); MKC Silica GS50Z andMKC Silica SS-15 (Mitsubishi Chemical Corp.), Admafine SOE-E3, AdmafineSO-C3, Admafine AO-800, Admafine AO-809, Admafine AO-500, and AdmafineAO-509 (Adomatex Co., Ltd.); M. S. GEL D-560A, M. S. GEL D-5120A, M. S.GEL D-5300A, M. S. GEL D-2060A, M. S. GEL D-20120A, M. S. GEL D-20-300A,SILDE-X H-31, SELDEX H-32, SILDEX H-51, SILDEX H-52, SILDEX H-121,SILDEX H-122, SILDEX L-31, SILDEX L-51, SILDEX L-121, SILD EX F-51, andSILDEX F-121 (Asahi Glass); SYLYSIA 250, SYLYSIA 250N, SYLYSIA 256,SYLYSIA 256N, SYLYSIEA 310, SYLYSIA 320, SYLYSIA 350, SYLYSIA 358,SYLYSIA 430, SYLYSIA 431, SYLYSIA 440, SYLYSIA 450, SYLYSIA 470, SYLYSIA435, SYLYSIA 445, SYLYSIA 436, SYLYSIA 446, SYLYSIA 456, SYLYSIA 530,SYLYSIA 540, SYLYSIA 550, SYLYSIA 730, SYLYSIA 740, SYLYSIA 770,SYLOPHOBIC100, and SYLOPHOBIC 200 (Fuji Silysia Chemical Co., Ltd.); andTismo-D, Tismo-L, Tofica Y, Tofica YN, Tofica YB, Dendol WK-200, DendolWK-200B, Dendol WK-300, Dendol BK-200, Dendol BK-300, Swanite, andBarihigh B Super Dendol (Otsuka Chemical Co., Ltd.).

The inorganic fillers may also be surface treated with a silane couplingagent. Silane coupling agents which can be used for this purpose includevinyl triclorosilane, vinyl tris (β-methoxyethoxy) silane,vinyltriethoxy silane, vinyltrimethoxy silane, γ-(methacryloxypropyl)trimethoxy silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxy silane,γ-glycydoxypropyltrimethoxy silane, γ-glycydoxypropylmethyl diethoxysilane, N-β(aminoethyl)yaminopropyltrimethoxy silane,N-β-(aminoethyl)-γ-aminopropylmethyldimethoxy silane,γ-aminopropyltriethoxysilane, N-phenyl-γ-amino propyl trimethoxy silane,γ-mercaptopropyl trimethoxysilane, and γ-chloropropyltrimethoxy silane.

The condition of the surface of the particles of the filler used and theimpurities contained in filler from the fabrication process can affectthe curing reaction of the resin composition. In such cases, it ispreferable to wash the filler particles or coat the particles with anappropriate primer as a method of improving the curing properties. Theinventors have also noted that certain fillers tend to contribute to aparticularly marked reduction in viscosity stability. Without wishing tobe bound by any particular theory, a hypothesized cause for thisphenomenon is the presence of residual acids present amongst theparticles of such fillers, which are an unwanted but often unavoidablebyproduct of the manufacturing process used to create them. Theseresidual acids will react with cationically polymerizable components inthe surrounding resin, resulting in partial polymerization and anincrease in viscosity over time.

The liquid radiation curable resin for additive fabrication can includeany suitable amount of inorganic filler or combination of fillers ascomponent (e), for example, in an amount up to about 80 wt % of theresin composition, in certain embodiments from about 30 to about 80 wt %of the resin composition, and in further embodiments from about 50 toabout 70 wt % of the resin composition. If the amount of the component(e) is too small, the water and heat resistant properties, durability,and structural rigidity of the molds made of the prepared resincomposition do not increase sufficiently. On the other hand, if theamount of the component (e) is too large, the fluidity of the preparedresin composition becomes too low, rendering it difficult or evenun-workable in additive fabrication processes. The excessive amount ofthe component (e) can also affect the time needed for radiation curingof the resin composition, causing the processing time to increasesubstantially.

Filled Matrix

The above inorganic fillers may be used singly or in combination of twoor more. As has been generally known to those skilled in the art, byusing inorganic fillers with different properties in combination, it ispossible to impart certain properties derived from the fillers to theprepared resin composition. Further, the prepared resin composition canhave different viscosities if the average grain size or fiber length, orthe grain size or fiber length distribution of the inorganic filler usedis different, though the substance and amount are the same. Therefore,by appropriately determining not only the average particle size or fiberlength but also the particle size or fiber length distribution, or byusing inorganic fillers of the same substance with different averageparticle sizes or fiber lengths in combination, the necessary amount ofthe filler and the fluidity and other properties of the prepared resincan be controlled as desired.

Presently, inventors have now surprisingly found that certain filled“matrices” are able to contribute to the formation of sufficientlyrobust three-dimensional solid parts yet stabilize the liquid radiationcurable composition for additive fabrication to impart improvedresistance to: (1) an unwanted particle settling into a soft pack orhard pack, and (2) an increase in viscosity over time. Such compositionsare henceforth referred to as “optimally stabilized”. For the purposesherein, “matrices” are defined as arrangements of inorganic fillerconstituents of varying sizes, substances, and/or size distributionswhich form a suspended solid lattice or backbone in a liquid radiationcurable composition for additive fabrication. A matrix of the presentinvention contains at least two constituents: (1) a microparticleconstituent that comprises a plurality of inorganic particles largelydefining the structure of the matrix; and (2) a nanoparticle constituentthat comprises a plurality of inorganic particles which fill gapsbetween successive microparticles in order to form a more fully filledmatrix.

The microparticle constituent contains inorganic microparticles havingan average particle size or fiber length of from about 1 to about 999micrometers (μm), more preferably from about 1 to about 50 μm, morepreferably from about 1 to about 10 μm, as measured in accordance withISO13320:2009. In an embodiment of the invention, the microparticleconstituent is spherical silica powder, such as of fused or crystalsilica. In an embodiment of the invention, the microparticles of themicroparticle constituent possess an average particle size or fiberlength of from about 2 to about 8 μm.

The nanoparticle constituent contains inorganic nanoparticles having anaverage particle size or fiber length of from about 1 to about 999nanometers (nm), more preferably from about 20 to about 200 nm, morepreferably from about 50 to about 100 nm, as measured in accordance withISO13320:2009. In an embodiment of the invention, the nanoparticleconstituent is spherical silica powder, such as fused or crystal silica,and possesses an average particle size or fiber length of from about 50to about 100 nm.

The microparticle constituent or nanoparticle constituent of the presentinvention may possess any particle size distribution. Thus, aconstituent may be deemed to fall within a range as herein describedeven though the “tails” of a particular particle size distribution falloutside that stated range, so long as the mean particle size fallswithin it.

Such particle sizes notwithstanding, inventors have discovered thatoptimally stabilized compositions may be achieved by selectingappropriately-sized microparticle and nanoparticle constituents relativeto each other. A derivation of the lower bound of the ratio of averageparticle size of the microparticles in the microparticle constituent tothe nanoparticles in the nanoparticle constituent in an embodiment ofthe invention is depicted in FIGS. 1 and 2. As FIGS. 1 and 2 representspecific matrix configurations, they are merely examples and are notintended to limit the scope of the invention. FIG. 1 depicts atwo-dimensional cross section of a square configuration filled matrix 1.The square configuration filled matrix 1 includes a microparticleconstituent 3 and a nanoparticle constituent 4. The microparticleconstituent 3 further comprises individual spherical microparticles 7,8, 9, and 10, whereas the nanoparticle constituent 4 comprises sphericalnanoparticles 11, 12, and 13. An imaginary square 2 encompasses thecenterpoints of the microparticles 7, 8, 9, and 10 to demonstrate moreclearly the square configuration of the filled matrix. In order toensure the possibility of a tightly packed, stabilized matrix, thenanoparticle radius 6 can only be large enough to form a nanoparticlewhich is tangential to the four surrounding, contacting microparticles.Thus the minimum ratio of the microparticle radius 5 to the nanoparticleradius 6 in such a configuration can be derived using the PythagoreanTheorem a²+b²=c², where a and b are equal to the microparticle radius 5,and c is equal to combined value of the microparticle radius 5 and thenanoparticle radius 6. Simplifying the expression yields c=√{square rootover (2)}, or further that the nanoparticle radius 6 is equal to(√{square root over (2)}−1) times the value of the microparticle radius5. Thus in this configuration, the minimum ratio of the average particlesize of the microparticle constituent to the average particle size ofthe nanoparticle constituent is

$\frac{1}{\sqrt{2} - 1},$

or approximately 2.41:1.

An alternative, more tightly-packed embodiment is depicted in FIG. 2.FIG. 2 involves a two-dimensional cross section of a triangularconfiguration filled matrix 14. The triangular configuration filledmatrix 14 includes a microparticle constituent 16 and a nanoparticleconstituent 17. The microparticle constituent 16 further comprisesspherical microparticles 18, 19, and 20, whereas the nanoparticleconstituent 17 comprises spherical nanoparticles 21, 22, 23, and 24. Animaginary equilateral triangle 15 encompasses the centerpoints of themicroparticles 18, 19, and 20, to demonstrate more clearly thetriangular configuration of the filled matrix. In order to ensure thepossibility of a tightly packed, stabilized matrix, the nanoparticleradius 26 can only be large enough to form a nanoparticle which istangential to the three surrounding, contacting microparticles. Thus theminimum ratio of the microparticle radius 25 to the nanoparticle radius26 in such a configuration can be derived using trigonometry, whereinthe nanoparticle radius 26 is equal to the expression

${\frac{r}{\cos \; 30{^\circ}} - r},$

where r is equal to the microparticle radius 25. Thus in thisconfiguration, the minimum ratio of the average particle size of themicroparticles in the microparticle constituent to the nanoparticles inthe nanoparticle constituent is

$\frac{1}{\frac{r}{\cos \; 30{^\circ}} - r},$

or approximately 6.46:1.

Thus, in an embodiment according to the present invention, the ratio ofthe average particle size of the microparticles in the microparticleconstituent to the nanoparticles in the nanoparticle constituent is fromabout 2.41:1 to about 2,000:1, more preferably from about 2.41 to about200:1, more preferably from about 6.46:1 to about 200:1, even morepreferably from about 6.46:1 to about 100:1. Ratios whereby the size ofthe average particle size of the microparticles in the microparticleconstituent to the nanoparticles in the nanoparticle constituent exceedsthese figures tend to produce unwieldy matrices that raise the viscosityof the overall composition with which they are associated, or, due to anexcessive average microparticle size, they do not enable sufficientresolution of solid parts cured therefrom. They may also contribute tounstable filled matrices which readily disintegrate into a soft pack.

The inventors have also surprisingly discovered that liquid radiationcurable resin compositions for additive fabrication may become optimallystabilized when the ratio by weight of the microparticle constituent tothe nanoparticle constituent is from greater than about 1:1 to about12:1, more preferably from about 4:1 to about 8:1. Compositions havinglower weight ratios tend not to form a matrix imparting sufficientmechanical rigidity and strength to the solid part upon curing.Conversely, those compositions having a microparticle constituent whichcomprises too large a weight percentage of the total filled matrix tendto form an unstable matrix which rapidly breaks down, causing theinorganic filler to settle into an unwanted hard or soft pack.

Additionally, inventors have discovered that the density of theconstituents of the filled matrices also can contribute to formulationof an optimally stabilized composition. Thus, inventors have alsodiscovered that liquid radiation curable resin compositions for additivefabrication may also become optimally stabilized when the ratio byvolume of the microparticle constituent to the nanoparticle constituentis from greater than about 1:1 to about 12:1, more preferably from about4:1 to about 8:1. Compositions having lower volume ratios tend not toform a matrix imparting sufficient mechanical strength to the mold uponcuring. Conversely, those compositions having a microparticleconstituent which comprises too large a percentage by volume of thetotal filled matrix tend to form an unstable matrix which rapidly breaksdown, causing the inorganic filler to settle into an unwanted hard orsoft pack.

Furthermore, the inventors have discovered that the respective numbersof particles of the constituents of the filled matrices also cancontribute to formulation of an optimally stabilized composition.Although matrices of the present invention may possess a greater amountof the microparticle constituent than the nanoparticle constituent byweight, they often possess a greater number of individual nanoparticlesthan microparticles, due to the markedly smaller weight of eachnanoparticle. Thus, inventors have also discovered that filled liquidradiation curable compositions for additive fabrication may also becomeoptimally stabilized when the ratio by number of the total amount ofnanoparticles in the nanoparticle constituent to the total amount ofmicroparticles in the microparticle constituent present is from about50:1 to about 1,000,000:1, more preferably from about 5,000:1 to about50,000:1. Compositions having too few or too many relative number ofnanoparticles to microparticles tend to form an unstable matrix whichcan break down, causing the inorganic filler to settle into a hard orsoft pack.

It is understood that the number of particles and overall volume of amatrix constituent may vary depending on the matrix constituent'sparticle size distribution. It is nonetheless assumed herein that forpurposes of calculating the “ratio by volume” or “ratio by number” thatall of the particles present for a given constituent possess the meanparticle size for that constituent, as determined by ISO13320:2009.

The aforementioned fillers, sizes, combinations, and ratios of filledconstituents form optimally stabilized compositions because theyprescribe filled matrices which maintain their original structure overtime, and resist ancillary polymerization. Although not wishing to bebound by any theory, it is hypothesized that such filled matricesachieve this technical effect because they are stabilized bothmechanically and chemically. That is, certain ratios of filled inorganicconstituents in a matrix prevent the matrix from disintegrating becausethe individual particles are physically prevented from significantmovement or sedimentation due to proper arrangements of interlockingmicroparticles and nanoparticles. Additionally, such sedimentation isfurther prevented because the constituents of the filled matrices of thepresent invention are arranged so as to optimize the chemical bondsformed both between successive constituent particles, and also betweenthe constituent particles and the surrounding liquid. This equilibriumof chemical bonds imparts additional stability and rigidity to theoverall filled matrix. The inventors have discovered that such optimallystabilized resins exhibit improved resistance to settling and viscosityincrease versus all other previously known filled liquid radiationcurable compositions suitable for certain additive fabricationapplications.

In addition to the aforementioned factors, inventors have alsodiscovered the surprisingly significant effect that the particledispersion pH further has on polymerization efficacy and viscositystability of the resulting photocurable composition for additivefabrication into which it is ultimately incorporated. Particledispersion pH is herein defined as the pH of the filled particledispersion—that is, the pH of the solution incorporating two elements:the filler constituent (for example, the nanoparticle constituent ormicroparticle constituent) and the solvent into which the solid fillerconstituent is incorporated. Non-limiting examples of commonly-used suchsolvents include inert agents such as methyl ethyl ketone orisopropanol, or polymerizable agents such as epoxies, oxetanes, or(meth)acrylates. Such solvents may be employed singularly or incombination of two or more. Particle dispersion pH is measured prior tothe incorporation of the filled particle dispersion into the liquidradiation curable resin composition for additive fabrication as a whole.

Inventors have discovered that if the particle dispersion pH fallswithin certain ranges, in particular the thermal stability of a liquidradiation curable composition for additive fabrication can be markedlyimproved. This is because the alkaline or acidic (as the case may be)nature of the filled particle dispersion causes it to interact with thepH of the entire surrounding resin, thereby influencing the efficacy andspeed of the cationic polymerization reaction during an additivefabrication process. If the particle dispersion pH is too low, theresulting resin may become too acidic, thereby initiating polymerizationreactions amongst the cationically curable components in the surroundingresin (such as epoxies and oxetanes) even in the absence of exposure toradiation. This unwanted effect in additive fabrication applications isparticularly increased at elevated temperatures, and greatly contributesto an increase in viscosity of the resultant resin over time.

Conversely, if the particle dispersion pH is too high, the resultingresin becomes too alkaline, thereby inhibiting photopolymerizationreactions altogether. In this scenario, the Brønsted acid speciesgenerated by the cationic photoinitiator component become neutralized bythe basic nature of the filled particle dispersion before said Brønstedacid species can initiate any photopolymerization reaction. Because thepresence of such Brønsted acid-generating species are necessary toinitiate and propagate the ring-opening reaction which is emblematic ofcationic polymerization, it is important that the particle dispersion pHis maintained sufficiently low.

In an embodiment, the particle dispersion pH is from 4.0 to 8.0. Inanother embodiment, the particle dispersion pH is from 5.5 to 7.5. Inanother embodiment, the particle dispersion pH is from 6.0 to 7.5. Inanother embodiment, the particle dispersion pH is greater than 5.5. Inanother embodiment, the particle dispersion pH is neutral, or about 7.0.

Notably, in prescribing filled matrices of the present invention, theinventors have arrived at liquid radiation curable compositions foradditive fabrication that also possess lower initial viscosities thanthose previously contemplated as practical. Particularly, nocompositions heretofore have been described that successfully combine adecreased initial viscosity with improved anti-sedimentationcharacteristics, given the longstanding belief of the inverselyproportional relationship between those characteristics as they pertainto liquid radiation curable compositions for additive fabrication. Priorcompositions might have been formulated for either low initial viscosityor anti-settling, but not both. Thus, it has heretofore been thoughtthat formulating a low-viscosity composition was diametrically opposedto creating one that minimized or eliminated filler settling behavior,because of the belief that the relatively high density inorganicparticles would rapidly phase separate when situated in a surroundingliquid medium of significantly lower density.

All things being equal, the viscosity of a liquid radiation curablecomposition for additive fabrication is inversely proportional to theaverage particle size of the filled particles immersed therein.Recognizing this principle, the inventors have contravened thelongstanding belief that precipitation of the filler occurs when theviscosity of the prepared resin into which it is immersed becomes toolow by prescribing particle sizes and ratios of the nanoparticle andmicroparticle constituents in a way according to the present inventionso as to create a low-viscosity, yet optimally stable matrix. Thus,inventors have been able to formulate a matrix filled, liquid radiationcurable resin for additive fabrication that surprisingly achieves a lowinitial viscosity, imparts sufficient mechanical properties in the curedparts derived therefrom, while simultaneously demonstrating improvedanti-sedimentation and viscosity stability.

Stabilizers and Other Components

Stabilizers are often added to the resin compositions in order tofurther prevent a viscosity build-up, for instance a viscosity build-upduring usage in a solid imaging process. Useful stabilizers includethose described in U.S. Pat. No. 5,665,792, the entire disclosure ofwhich is hereby incorporated by reference. In the instant claimedinvention, the presence of a stabilizer is optional. In a specificembodiment, the liquid radiation curable resin composition for additivefabrication comprises from 0.1 wt % to 3% of a stabilizer.

If present, such stabilizers are usually hydrocarbon carboxylic acidsalts of group IA and IIA metals. Most preferred examples of these saltsare sodium bicarbonate, potassium bicarbonate, and rubidium carbonate.Solid stabilizers are generally not preferred in filled resincompositions. If present, a 15˜23% sodium carbonate solution ispreferred for formulations of this invention with recommended amountsvarying between 0.05 to 3.0% by weight of resin composition, morepreferably from 0.05 to 1.0 wt %, more preferably from 0.1 to 0.5% byweight of resin composition. Alternative stabilizers includepolyvinylpyrrolidones and polyacrylonitriles.

Other possible additives include dyes, pigments, antioxidants, wettingagents, photosensitizers for the free-radical photoinitiator, chaintransfer agents, leveling agents, defoamers, surfactants and the like.

The liquid radiation curable resin composition for additive fabricationof the invention can further include one or more additives selected fromthe group consisting of bubble breakers, antioxidants, surfactants, acidscavengers, pigments, dyes, thickneners, flame retardants, silanecoupling agents, ultraviolet absorbers, resin particles, core-shellparticle impact modifiers, soluble polymers and block polymers.

The second aspect of the claimed invention is a process of forming athree-dimensional object comprising the steps of forming and selectivelycuring a layer of the liquid radiation curable resin compositionaccording to the present invention as described herein with actinicradiation and repeating the steps of forming and selectively curing alayer of the liquid radiation curable resin composition for additivefabrication as described herein a plurality of times to obtain athree-dimensional object.

As noted previously herein, it is preferred that filled liquid radiationcurable compositions for additive fabrication have a low initialviscosity in order to maximize workability and minimize processing time.Therefore, it is preferred that liquid radiation curable compositionsfor additive fabrication according to the present invention have aviscosity, when measured at 30 degrees Celsius, of between 200centipoise (cPs) and 2000 cPs, more preferably between 500 cPs and 1500cPs, even more preferably between 600 cPs and 1200 cPs.

Furthermore, the filled composition must be able to impart sufficientstrength and stiffness into the three dimensional solid objects whichthey form upon curing. Therefore, it is preferred that liquid radiationcurable compositions for additive fabrication according to the presentinvention have a flexural modulus, after full cure with actinicradiation and a 60 minute UV and thermal postcure according to processeswell-known in the art of additive fabrication and stereolithography(ASTM D648-98c), of at least 6,000 MPa, more preferably at least about8,000 MPa, and even more preferably at least about 10,000 MPa. In anembodiment of the present invention, the flexural modulus achieved isbetween about 8,000 MPa and about 12,000 MPa.

Additionally, the filled composition must be able to impart sufficientresilience and integrity into three dimensional solid objects which theyform upon curing, even after exposure to high heat conditions. Thus, itis preferred that the liquid radiation curable composition for additivefabrication according to the present invention, after full cure withactinic radiation and 60 minute UV and thermal postcure according toprocesses well-known in the art of additive fabrication andstereolithography (ASTM D648-98c), has a heat distortion temperature at1.82 MPa of at least about 80 degrees Celsius, more preferably at leastabout 100 degrees Celsius, and more preferably at least about 110degrees Celsius. In an embodiment of the present invention, the heatdistortion temperature at 1.82 MPa is between about 80 degrees Celsiusand about 120 degrees Celsius.

The third aspect of the claimed invention is the three-dimensionalobject formed from the liquid radiation curable resin of any one of thefirst aspect of the present invention, by the process of the secondaspect of the claimed invention.

The fourth aspect of the claimed invention is a liquid radiation curableresin for additive fabrication comprising:

(f) a cationically polymerizable component;

(g) a (meth)acrylate component;

(h) a cationic photoinitiator;

(i) a free-radical photoinitiator; and

(j) a filled matrix, further comprising

-   -   a filled particle dispersion containing        -   a nanoparticle constituent made up of a plurality of silica            nanoparticles having an average particle size of at least            about 50 nanometers, and a solvent, and    -   a microparticle constituent made up of a plurality of inorganic        microparticles;    -   wherein the ratio by weight of the microparticle constituent to        the nanoparticle constituent is from about 1:1 to about 12:1;        and    -   wherein the filled particle dispersion has a particle dispersion        pH of greater than about 5.5.

The following examples further illustrate the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLES

These examples illustrate embodiments of the liquid radiation curableresins for additive fabrication of the instant invention. Table 1describes the various components of the liquid radiation curable resinsfor additive fabrication used in the present examples.

TABLE 1 Function in Supplier/ Component Formula Chemical DescriptorManufacturer 4-methoxyphenol Antioxidant 4-methoxyphenol Sigma- AldrichDG-0071 Stabilizer Saturated sodium carbonate in water DSM solutionDesotech Aerosil 200 Settling Hydrophilic fumed silica Evonik additiveIndustries Chivacure 1176 Cationic A mixture of: bis[4- ChitecPhotoinitiator diphenylsulfoniumphenyl]sulfide bishexafluoroantimonate;thiophenoxyphenylsulfonium hexafluoroantimonate and propylene carbonate.Irgacure 184 Radical 1-Hydroxy-1-cyclohexyl phenyl BASF Photoinitiatorketone DPHA Radically Dipentaerythritol hexaacrylate Sigma-Polymerizable Aldrich Compound Heloxy 68 Cationically Neopentylglycoldiglycidyl ether Momentive Polymerizable compound Erisys GE 22Cationically 1,4 Cyclohexanedimethanol Emerald Polymerizable DiglycidylEther Performance Compound Materials Celloxide 2021P Cationic3,4-Epoxycyclohexylmethyl 3′,4′- Daicel Polymerizableepoxycyclohexanecarboxylate Corporation Compound HQMME SyntheticHydroquinone monomethyl ether Nova intermediate, International uvinhibitor SR 351 Radically Trimethylolpropane triacrylate SartomerPolymerizable Compound ORGANO- Filled particle 30% colloidal silicananoparticles in Nissan SILICASOL dispersion 70% methyl ethyl ketonesolvent; Chemical MEK-AC-2101 including 10-15 nm particle sizedistribution nanoparticle constituent ORGANO- Filled particle 30%colloidal silica nanoparticles in Nissan SILICASOL dispersion 70% methylethyl ketone solvent; Chemical MEK-AC-4101 including 40-50 nm particlesize distribution nanoparticle constituent ORGANO- Filled particle 30%colloidal silica nanoparticles in Nissan SILICASOL dispersion 70% methylethyl ketone solvent; Chemical MEK-AC-5101 including 70-100 nm particlesize distribution; nanoparticle 80 nm avg. particle size constituentORGANO- Filled particle 30% colloidal silica nanoparticles in NissanSILICASOL dispersion Isopropanol solvent; 70-100 nm Chemical IPA-ST-ZLincluding particle size distribution nanoparticle constituent DZ-0077Filled particle 40% colloidal silica nanoparticles in Nanoparticlesdispersion 60% 3,4-epoxycyclohexylmethyl from Nissan including3′,4′-epoxycyclohexanecarboxylate; Chemical; nanoparticle 80 nm avg.particle size Epoxy from constituent Daicel Nanopox A 610 Filledparticle 40% spherical silica nanoparticles in Evonik dispersion 60%3,4-epoxycyclohexylmethyl Industries including 3′,4′-epoxycyclohexanecarboxylate; nanoparticle 20 nm avg. particle sizeconstituent Sunspacer 04.X Filled particle SiO2 Particle (4 μm averageparticle Suncolor dispersion size) including microparticle constituentNP-30S Filled particle Spherical SiO₂ microparticles; 4 μm AGCdispersion avg. particle size Chemicals including microparticleconstituent

Examples 1-12

Various filled liquid radiation curable resins for additive fabricationwere prepared according to well-known methods in the art, employing ahybrid cure photoinitiating package, a cationically polymerizablepackage, a radically polymerizable package, and select additives. TheMEK-AC-5101 nanoparticles are supplied in a methyl ethyl ketone solvent,which was exchanged for a cycloaliphatic epoxide—resulting in a 40%nanoparticle/60% epoxide solution—using standard techniques. Other resincompositions utilizing varying filled matrices were then prepared byalternating the type and/or quantity of microparticle constituent andnanoparticle constituent.

These samples were tested according to the methods for viscosity,settling behavior, shelf life thermal stability, and physical propertytesting, as detailed below. Finally, filled matrix characteristics weredetermined by calculating the ratio by weight, size, and volume of themicroparticle constituent to the nanoparticle constituent, and the ratioby particle number of the nanoparticle constituent to the microparticleconstituent. The results are presented in Table 2.

Viscosity

The viscosity of each sample was taken with an Anton Paar RheoplusRheometer (S/N 80325376) using a Z3/Q1 measuring cylinder (S/N 10571)with a 25 mm diameter. The temperature was set at 30° Celsius with ashear rate of 50 s⁻¹. The rotational speed was set at 38.5 min⁻¹. Themeasuring container was a H-Z3/SM cup (diameter 27.110 mm) which wasfilled with 21.4 grams of sample (enough to the spindle). Measurementswere recorded in millipascal-seconds (mPa·s), but converted and reportedherein as centipoise (cPs).

Settling Behavior of Filled Materials

Forty grams of each sample was measured into a glass petri dish andplaced in a 50 degrees Celsius (C)±2 degrees C. oven. At the appropriateinterval each sample was removed from the oven, and qualitativelyexamined for settling behavior. The behaviors observed were no settling,soft pack, or hard pack. Samples were then placed back into the oven toresume the test for the duration of the prescribed allotted time(typically 28 days). The duration at which the first indication of softpack or hard pack settling behavior was observed was then recorded.

Viscosity Stability—Shelf Life Thermal Stability Test

Forty grams of each sample was measured and placed in a 50 degreesCelsius (C)±2 degrees C. oven. At the appropriate interval each samplewas removed from the oven, then placed in a centrifuge at 2500 rpm for 1minute (to remix any separation that might have occurred) and had theviscosity taken according the viscosity method. Samples were then placedback into the oven to resume the test for the duration of the prescribedallotted time (typically 28 days). Measurements were recorded inmillipascal-seconds (mPa·s), but converted and reported herein ascentipoise (cPs). Sections marked with an asterisk (*) indicates thatbecause partial gelling of the sample had occurred, accurate readingswere not obtainable.

Physical Property Testing

Samples were built by viper SLA machine (S/N 03FB0244 or S/N 02FB0160)to the standard Type I dogbone shape for tensile testing where theoverall length is 6.5 inches, the overall width is 0.75 inch and thethickness is 0.125 inches and standard bar shape for the Flexuraltesting where the length is 5 inches, the overall width is 0.5 inch andthe thickness is 0.125 inches. Samples were conditioned 7 days at 23° C.at 50% relative humidity. The tensile properties were tested accordingto the ASTM D638-10 test method. The flexural strength & modulusproperties were tested according to the ASTM D 0790 test method. Bothtests were performed on the 5G Sintech tensile tester (S/N 34359).

Ratios by Size, Weight, Volume, and Number

The ratio by size was derived by dividing the mean particle size of themicroparticle constituent in a given composition by the mean particlesize of the nanoparticle constituent in that composition. Mean particlesizes were determined from ISO13329:2009. Values expressed do notpossess units.

The ratio by weight was derived by dividing the total amount by weightof the microparticle constituent in a given composition by the totalamount by weight of the nanoparticle constituent in that composition.Values expressed do not possess units.

The ratio by volume was derived by dividing the total volume of themicroparticle constituent in a given composition by the total volume ofthe nanoparticle constituent present in that composition. Volume for aconstituent was determined by dividing the weight of that constituent byits density. Where, as in the examples below, both the microparticleconstituent and nanoparticle constituent possess the same density, itshould be noted that the ratio by volume does not differ from the ratioby weight. Values expressed do not possess units.

The ratio by number was derived by dividing the total number ofnanoparticles present in the nanoparticle constituent by the totalnumber of microparticles present in the microparticle constituent.Where, as in the examples below, spherical particles were used, for thesake of calculation, it was assumed that each matrix constituent wascomprised entirely of spherical particles possessing a symmetricparticle size distribution about the mean particle size. Thus,calculations were performed by first determining the volume of eachspherical particle, which can be derived by the formula V=4/3πr³, wherer is the radius of the spherical particle. Next, the weight of eachspherical particle was determined by multiplying the volume of eachparticle by its density. Where, as in the examples below, both themicroparticle constituent and nanoparticle constituent possess the samedensity, the relative value of the density is immaterial to the ratiocalculation. Finally, the value of the weight of each particle wasdivided by the total weight in the entire composition of the constituentof which that particle was included, to obtain the total number ofparticles present in the composition. Calculations were similarlyperformed on the other matrix constituents to determine the ratio ofparticles by number. Values expressed do not possess units.

TABLE 2 Values are listed in parts by weight Formula Component Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Aerosil 200 0.37 0.370.37 0.37 0.37 0.37 Chivacure 1176 3.80 3.80 3.80 3.80 3.80 3.80 DPHA2.07 2.07 2.07 2.07 2.07 2.07 Heloxy 68 7.500 7.500 7.500 7.500 7.5007.500 HQMME 0.018 0.018 0.018 0.018 0.018 0.018 IRGACURE 184 0.400 0.4000.400 0.400 0.400 0.400 SR 351 3.350 3.350 3.350 3.350 3.350 3.350DZ-0077 0 34.610 27.000 19.500 10.000 10.000 Nanopox A 610 34.610 0 0 00 0 Celloxide 2021P 0 0 4.61 9.11 14.85 18.61 NP-30 47.890 47.890 50.8953.89 57.65 53.89 TOTAL 100.00 100.00 100.00 100.00 100.00 100.00 Ratioby size  200:1   50:1   50:1   50:1   50:1   50:1 (micro/nano) Ratio byweight 3.46:1 3.46:1 4.71:1 6.91:1 14.41:1 13.47:1 (micro/nano) Ratio byvolume 3.46:1 3.46:1 4.71:1 6.91:1 14.41:1 13.47:1 (micro/nano) Ratio by# 2,312,633:1    36,135:1  26,528:1  18,092:1  8,673:1 9,278:1(nano/micro) Initial Viscosity 2712 1171 1132 1225 1556 1315 Viscosity,1 week 3698 1646 1630 1767 2307 1926 Viscosity, 2 weeks 4333 1733 17551721 * * Viscosity, 3 weeks 5072 * * 1921 * * Viscosity, 4 weeks6203 * * * * * Settling Behavior, Soft Pack Soft Pack Soft Pack SoftPack Hard Pack Hard Pack type Settling Behavior, 3 15 15 11 11 11 timing(days) Formula Component Example 7 Example 8 Example 9 Example 10Example 11 Example 12 Aerosil 200 0.37 0.37 0.37 0.37 0.37 0.37Chivacure 1176 3.80 3.80 3.80 3.80 3.80 3.80 DPHA 2.07 2.07 2.07 2.072.07 2.07 Heloxy 68 7.500 7.500 7.500 7.500 7.500 7.500 HQMME 0.0180.018 0.018 0.018 0.018 0.018 Irgacure 184 0.400 0.400 0.400 0.400 0.4000.400 SR 351 3.350 3.350 3.350 3.350 3.350 3.350 DZ-0077 10.000 10.00027.000 19.500 0 0 Nanopox A 610 0 0 0 0 0 0 Celloxide 2021P 21.61 24.617.61 15.11 24.85 34.61 NP-30 50.89 47.89 47.89 47.89 57.65 47.890 TOTAL100.00 100.00 100.00 100.00 100.00 100.00 Ratio by size   200:1   50:1  50:1   50:1 Undefined Undefined (micro/nano) Ratio by weight 12.72:111.97:1 4.43:1 6.14:1 Undefined Undefined (micro/nano) Ratio by volume12.72:1 11.97:1 4.43:1 6.14:1 Undefined Undefined (micro/nano) Ratio by# 9,825:1 10,441:1  28,190:1  20,359:1  0 0 (nano/micro) InitialViscosity 1133 918.3 1036 936 2182 1098 Viscosity, 1 week 1619 1307 14081286 3370 1590 Viscosity, 2 weeks * * 1428 * * * Viscosity, 3weeks * * * * * * Viscosity, 4 weeks * * * * * * Settling Behavior, HardPack Hard Pack Soft Pack Soft Pack Hard Pack Hard Pack type SettlingBehavior, 11 11 15 15 11 11 timing

Examples 13-20

Various base filled resin compositions for additive fabrication wereprepared according to well-known methods in the art by combining aphotoinitiating package, a cationically polymerizable package, aradically polymerizable package, and select additives. Other resincompositions utilizing varying filled matrices were then prepared byalternating the type and/or quantity of microparticle constituent andnanoparticle constituent. Additionally, a cationically polymerizablecomponent was varied. These samples were tested according to the methodsprescribed herein for viscosity and settling behavior. Finally, filledmatrix characteristics were determined by calculating the ratio byweight and volume of the microparticle constituent to the nanoparticleconstituent, and the ratio by particle number of the nanoparticleconstituent to the microparticle constituent. The results are presentedin Table 3.

TABLE 3 Values are listed in parts by weight Component Ex. 13 Ex. 14 Ex.15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Aerosil 200 0.370 0.370 0.3700.370 0.370 0.370 0.370 0.370 DPHA 2.070 2.070 2.070 2.070 2.070 2.0702.070 2.070 Heloxy 68 7.500 7.500 7.500 7.500 Nanopox A 34.610 34.61010.000 10.000 610 NP-30 47.890 47.890 57.570 47.890 47.890 57.570 57.57057.570 SR 351 3.350 3.350 3.350 3.350 3.350 3.350 3.350 3.350 Celloxide14.810 14.810 14.810 14.810 2021P DZ-0077 34.610 34.610 10.000 10.000Erisys GE 7.500 7.500 7.500 7.500 22 Chivacure 4.210 4.210 4.330 4.2104.210 4.330 4.330 4.330 1176 + Irgacure 184 TOTALS 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 Ratio by  200:1  200:1   200:1   50:1  50:1   50:1   200:1   50:1 size (micro/nano) Ratio by 3.46:1 3.46:114.39:1 3.46:1 3.46:1 14.39:1 14.39:1 14.39:1 weight (micro/nano) Ratioby 3.46:1 3.46:1 14.39:1 3.46:1 3.46:1 14.39:1 14.39:1 14.39:1 volume(micro/nano) Ratio by # 2,312,633:1    2,312,633:1    555,845:1 36,135:1  36,135:1  8,685:1 555,845:1  8,685:1 (nano/micro) SettlingSoft Pack Soft Pack Hard Pack Soft Pack Soft Pack Hard Pack Hard PackHard Pack Behavior, type Settling 11 11 18 28 18 7 11 2 Behavior, timing

Examples 21-24

Various filled particle dispersions were evaluated to determine theparticle dispersion pH of the raw material (nanoparticle constituentplus solvent). Readings for each respective filled particle dispersionwere taken at 20° C. Before use, the electrode probe of a BeckmanCoulter Φ250 pH meter (Series #3527) was soaked in a pH 4 buffersolution overnight. The pH meter was calibrated with three standard pHbuffer solutions (pH 4.0, 7.0, and 10.01) before taking measurements.The calibration method and pH reading were performed according to themeter's operation instructions (Beckman Φ200 Series Operation Manual,pp. 19-21). After calibration, the probe was cleaned with distilledwater and then was gently tapped to remove any water residue. The glasswas not wiped vigorously in order to avoid scratches and dehydration.

In order to accurately measure the particle dispersion pH of the rawmaterial, it was necessary to first dissolve the filled particledispersion into a testing carrier (itself consisting of a 3:2 ratio ofdistilled water to methanol). Thus, 8.33 g of each filled particledispersion was dissolved into 43.75g of the testing carrier.

Next, the electrode probe of the Beckman Φ250 pH meter was inserted intothe above solution (filled particle dispersion plus testing carrier) toestablish a first particle dispersion pH reading. With the readingrecorded, the electrode probe was cleaned with a solution of 50% acetoneand 50% isopropanol (IPA) followed by distilled water. This cleaningprocedure was repeated between each of five separate readings taken foreach sample. The above process was repeated for each of four samples.The average value of the five readings for each of the four samples isreproduced in Table 4 below.

TABLE 4 Particle Size Particle Filled particle Distribution dispersiondispersion Solvent SiO₂ % (nm) pH Ex. 21 MEK-AC-2101 MEK 30 10-15  6.71Ex. 22 MEK-AC-4101 MEK 30 40-50  4.59 Ex. 23 IPA-ST-ZL IPA 30 70-1004.03 Ex. 24 MEK-AC-5101 MEK 30 70-100 7.34

Examples 25-29

New samples were then prepared by exchanging the original solvent in thesame four commercially available filled particle dispersions used inexamples 21-24 with a 3,4-epoxycyclohexylmethyl3′,4′-epoxycyclohexanecarboxylate solvent. This solvent exchange,accomplished according to standard techniques, resulted in a 40% silicananoparticle/60% epoxide solution. The pH of these resulting filledparticle dispersions were then recorded for each sample according to thetechnique illustrated in the discussion of Examples 21-24, supra, withthe exception that instead of creating a 8.33:43.75 filled particledispersion to test carrier solution, 6.25g of the resulting filledparticle dispersion was dissolved into 43.75g of the testing carrier.

Next, the samples were subjected to a thermal aging test. To effectuatethis test, the initial viscosity was first measured according to theviscosity testing procedure outlined in the discussion of examples 1-12,supra. After 7 days of aging in a 55° C. oven, samples were cooled toroom temperature and remixed if nanoparticle settling was observed.Viscosity was then again measured according to the viscosity testingprocedure outlined in the discussion of examples 1-12, supra.

TABLE 5 Component Ex. 25 Ex. 26 Ex. 27 Ex. 28 Ex. 29 Celloxide 2021P 060 60 60 60 Nanopox A610 100 0 0 0 0 MEK-AC-2101 0 40 0 0 0(nanoparticle constituent only) MEK-AC-4101 0 0 40 0 0 (nanoparticleconstituent only) IPA-ST-ZL 0 0 0 40 0 (nanoparticle constituent only)MEK-AC-5101 0 0 0 0 40 (nanoparticle constituent only) Resultingparticle 6.63 6.71 5.36 4.79 7.19 dispersion pH (post solvent exchange)Initial Viscosity 2750 1553 Gelled during 505 Viscosity, 7 days 532531000 solvent exchange 526 Viscosity Change 94% 1922% 4% (%)

Examples 30-31

Two filled liquid radiation curable resins for additive fabrication wereprepared according to well-known methods in the art, employing anidentical hybrid cure photoinitiating package, cationicallypolymerizable package, radically polymerizable package, and selectadditives. The only difference between the two samples was the identityof the nanoparticle constituent. E_(c), D_(p), and E₁₀ values weremeasured according to the working curve measurement procedure outlinedbelow. Further, the samples were subjected to the thermal aging testoutlined in the description of Examples 25-29, supra. Viscositymeasurements were taken (according to the procedure outlined in thediscussion of examples 1-12 herein, supra) at the beginning of the test,then again at 7 and 14 days at 55° C., with the results recorded inTable 6 below.

Working Curve Measurement

Working curve data (E_(c), D_(p), and E₁₀) was prepared using a solidstate laser operating at a wavelength of 354.7 nm in accordance with thebelow method.

The working curve is a measure of the photospeed of the particularmaterial. It represents the relationship between the thickness of alayer of liquid radiation curable resin produced as a function of theexposure given. For all formulations, the exposure-working curve of theformula is determined using methods well known in the art.

The exposure response for each formulation is measured using a 21.7 gsample of the formulation in a 100 mm diameter petri dish held at 30° C.and 30% RH. The surface of the formulation is exposed with the indicatedlight source. The exposures are made in half-inch squares (exposureregions) which are scanned out by drawing consecutive parallel linesapproximately 25.4 microns apart on the surface of the liquid in thepetri dish at 72 mW. Different exposure regions are exposed to differentlevels of known incident energy to obtain different cured thicknesses.The spot diameter at the liquid surface is approximately 0.0277 cm indiameter. After waiting at least 15 minutes for the exposed panels toharden, the panels are removed from the petri dish and excess, uncuredresin is removed by blotting with a Kimwipe EX-L (Kimberly Clark). Filmthickness is measured with a Mitutoyo Model ID-C 1 12CE IndicatorMicrometer. Film thickness is a linear function of the natural logarithmof the exposure energy; the slope of the regression is D_(p) (units ofmicron or mil) and E_(c) is the x-axis intercept of the regression fit(units of mJ/cm²). E₁₀ is the energy required to cure a ten mil (254micron) layer.

TABLE 6 Component Ex. 30 Ex. 31 Nanopox A 610 34.61 Dispersion ofExample 29 34.61 Erysis GE-20 7.5 7.5 SR-351 3.36 3.36 DPHA 2.07 2.07Irgacure 184 0.4 0.4 Chivacure 1176 3.8 3.8 4-methoxyphenol 0.02 0.02Aerosil 200 0.22 0.22 Sunspacer 04.X 47.87 47.87 DG-0071 0.15 0.15 Total100.00 100.00 Total fillers 61.71 61.71 Ec (mJ/cm2) 12.22 10.86 Dp(mils) 5.15 4.75 E₁₀ (mJ/cm2) 85 89.1 Initial Viscosity (30° C., cps)2282 1306 Viscosity (30° C., cps) (55° C., 7 days) 3899 1835 Viscosity(30° C., cps) (55° C., 14 days) 5405 2034

Discussion of Results

Examples 1-31 are matrix filled liquid radiation curable resincompositions demonstrating increased suitability for additivefabrication. It is apparent from Tables 2 and 3 that the ratio of themicroparticle constituent to the nanoparticle constituent (by weightand/or volume), is critical to creating filled matrices which can resistthe hard pack settling phenomenon. Particularly, it is noted that belowapproximately a 12:1 weight or volume ratio of the microparticleconstituent to nanoparticle constituent, filled matrices display asurprisingly improved tendency to withstand disintegration into a hardpack. The hard pack phenomenon is similarly evident in Examples 11 and12, wherein the nanoparticle constituent is removed from the filledmatrix entirely. Thus, in an embodiment of the present invention, thepresence of both a nanoparticle constituent and a microparticleconstituent is necessary to prevent unwanted hard pack phase separation.

Furthermore, Examples 1-20 demonstrate that when the ratio by number ofthe nanoparticles present in the nanoparticle constituent to themicroparticles present in the microparticle constituent becomes toolarge, the filled matrix can possess an undesirably high viscosity andquickly break down into a soft pack. Particularly, it is hypothesized,drawing upon support from the Examples in Tables 2 and 3, that filledmatrices become unwieldy and break down into a soft pack when the ratioof nanoparticles present in the nanoparticle constituent to the numberof microparticles present in the microparticle constituent is exceedsabout 1,000,000:1.

Additionally, Examples 21-31 demonstrate the effect that both theparticle dispersion pH and the particle size of the filled particledispersion have on the resulting liquid radiation curable composition'sthermal stability. It is surmised from an extrapolation of the data inTables 4-5 that below a particle dispersion pH of about 5.5, the acidicfilled particle dispersion imparts poor thermal stability into thephotocurable composition for additive fabrication into which it isincorporated, such that even a routine solvent exchange is impractical.Furthermore, from Table 6, it is shown that compositions possessing ananoparticle constituent with nanoparticles having an average particlesize of above 50 nm exhibit improved thermal stability versus thosehaving nanoparticles with an average size of below 50 nm, even where theparticle dispersion pH is in an otherwise acceptable range.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventor for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventor expects skilled artisans to employ such variations asappropriate, and the inventor intends for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one of ordinaryskill in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the claimedinvention.

What is claimed is:
 1. A liquid radiation curable composition foradditive fabrication comprising: (a) a cationically polymerizablealiphatic epoxide; (b) a multifunctional (meth)acrylate component; (c) acationic photoinitiator; (d) a free-radical photoinitiator; and (e) afilled matrix comprising a nanoparticle constituent comprising aplurality of inorganic nanoparticles, and a microparticle constituentcomprising a plurality of inorganic microparticles; wherein the ratio byweight of the microparticle constituent to the nanoparticle constituentis from about 1:1 to about 12:1; and wherein the ratio of the averageparticle size of the inorganic microparticles in the microparticleconstituent to the average particle size of the inorganic nanoparticlesin the nanoparticle constituent is from about 2.41:1 to about 200:1. 2.The liquid radiation curable composition for additive fabrication ofclaim 1, wherein the inorganic nanoparticles of the nanoparticleconstituent have an average particle size of from about 50 nanometers toabout 100 nanometers; and the inorganic microparticles of themicroparticle constituent have an average particle size of from about 2microns to about 8 microns.
 3. The liquid radiation curable compositionfor additive fabrication of claim 2, wherein at least one of themicroparticle constituent or the nanoparticle constituent comprisesspherical particles selected from the group consisting of ceramics,glass, and metal.
 4. The liquid radiation curable composition foradditive fabrication of claim 3, wherein the ratio by weight of themicroparticle constituent to the nanoparticle constituent is from about4:1 to about 8:1; and the ratio of the average particle size of theinorganic microparticles in the microparticle constituent to the averageparticle size of the inorganic nanoparticles in the nanoparticleconstituent is from about 6.46:1 to about 100:1.
 5. The liquid radiationcurable composition for additive fabrication claim 4, wherein thealiphatic epoxide component is a cycloaliphatic epoxy selected from thegroup consisting of:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)-cyclohexane-1,4-dioxane,bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide,4-vinylepoxycyclohexane, vinylcyclohexene dioxide,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,3,4-epoxy-6-methylcyclohexyl-3′,4′-epoxy-6′-methylcyclohexanecarboxylate,ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylates, trimethylcaprolactone-modified3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylates,β-methyl-δ-valerolactone-modified3,4-epoxycyclohexcylmethyl-3′,4′-epoxycyclohexane carboxylates,methylenebis(3,4-epoxycyclohexane), bicyclohexyl-3,3′-epoxide,bis(3,4-epoxycyclohexyl) with a linkage of —O—, —S—, —SO—, —SO₂—,—C(CH₃)₂—, —CBr₂—, —C(CBr₃)₂—, —C(CF₃)₂—, —C(CCl₃)₂—, or —CH(C₆H₅)—,dicyclopentadiene diepoxide, di(3,4-epoxycyclohexylmethyl) ether ofethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), andepoxyhexahydrodioctylphthalate.
 6. The liquid radiation curablecomposition for additive fabrication of claim 5, wherein the ratio byvolume of the microparticle constituent to the nanoparticle constituentis from about 1:1 to about 12:1.
 7. The liquid radiation curablecomposition for additive fabrication of claim 6, wherein the ratio bynumber of the inorganic nanoparticles in the nanoparticle constituent tothe inorganic microparticles in the microparticle constituent is fromabout 50:1 to about 1,000,000:1.
 8. The liquid radiation curablecomposition for additive fabrication of claim 7, wherein the ratio bynumber of the inorganic nanoparticles in the nanoparticle constituent tothe inorganic microparticles in the microparticle constituent is fromabout 5,000:1 to about 50,000:1.
 9. The liquid radiation curablecomposition for additive fabrication of claim 7, wherein, relative tothe total weight of the entire composition: component (a) is present inan amount of from about 10 wt % to about 30 wt %; component (b) ispresent in an amount of from about 2 wt % to about 10 wt %; component(c) is present in an amount of from about 1 wt % to about 10 wt %;component (d) is present in an amount of from about 0.1 wt % to about 5wt %; and component (e) is present in an amount of from about 30 wt % toabout 80 wt %.
 10. The liquid radiation curable composition for additivefabrication of claim 9, further comprising a multifunctional glycidylether that is devoid of cyclohexane groups.
 11. The liquid radiationcurable composition for additive fabrication of claim 10, wherein themultifunctional glycidyl ether that is devoid of cyclohexane groups is aneopentyl glycol diglycidyl ether.
 12. The liquid radiation curablecomposition for additive fabrication of claim 11 further comprising anoxetane, and wherein component (c) is an R-substituted aromaticthioether triaryl sulfonium or iodonium tetrakis(pentafluorophenyl)borate cationic photoinitiator with a tetrakis(pentafluorophenyl)borateanion and a cation of the following formula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.
 13. The liquid radiation curable composition of claim 11further comprising an oxetane, wherein component (c) possesses an anionrepresented by SbF₆ ⁻, PF₆ ⁻, BF₄ ⁻, (CF₃CF₂)₃PF₃ ⁻, (C₆F₅)₄B⁻,((CF₃)₂C₆H₃)₄B⁻, (C₆F₅)₄Ga⁻, ((CF₃)₂C₆H₃)₄Ga⁻,trifluoromethanesulfonate, nonafluorobutanesulfonate, methanesulfonate,butanesulfonate, benzenesulfonate, or p-toluenesulfonate, and a cationof the following formula (II):

wherein in formula (II), R¹, R², R³, R⁵ and R⁶ each independentlyrepresent an alkyl group, a hydroxy group, an alkoxy group, analkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group, anaryloxycarbonyl group, an arylthiocarbonyl group, an acyloxy group, anarylthio group, an alkylthio group, an aryl group, a heterocyclichydrocarbon group, an aryloxy group, an alkylsulfinyl group, anarylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, ahydroxy(poly)alkyleneoxy group, an optionally substituted amino group, acyano group, a nitro group, or a halogen atom, R⁴ represents an alkylgroup, a hydroxy group, an alkoxy group, an alkylcarbonyl group, analkoxycarbonyl group, an acyloxy group, an alkylthio group, aheterocyclic hydrocarbon group, an alkylsulfinyl group, an alkylsulfonylgroup, a hydroxy(poly)alkyleneoxy group, an optionally substituted aminogroup, a cyano group, a nitro group, or a halogen atom, m¹ to m⁶ eachrepresent the number of occurrences of each of R¹ to R⁶, m¹, m⁴, and m⁶each represent an integer of 0 to 5, and m², m³, and m⁵ each representan integer of 0 to
 4. 14. The liquid radiation curable composition foradditive fabrication of claim 11, wherein the composition has aviscosity of between about 600 cPs and about 1200 cPs, and after fullcure with actinic radiation and 60 min UV and thermal postcure, has thefollowing properties: (a) a heat distortion temperature at 1.82 MPa ofbetween about 80 degrees C. and about 120 degrees C., and (b) a flexuralmodulus of between about 8,000 MPa and about 12,000 MPa.
 15. The liquidradiation curable composition of claim 11, further comprising a secondaliphatic epoxide component, and wherein the microparticle constituentconsists of colloidal silica microparticles, and the nanoparticleconstituent consists of colloidal silica nanoparticles.
 16. A process offorming a three-dimensional object comprising the steps of forming andselectively curing a layer of the liquid radiation curable resincomposition for additive fabrication of claim 1 with actinic radiationand repeating the steps of forming and selectively curing a layer of theliquid radiation curable resin composition for additive fabrication ofclaim 1 a plurality of times to obtain a three-dimensional object. 17.The process of claim 15 wherein the source of actinic radiation is oneor more LEDs emitting a wavelength of from 340 nm-415 nm, preferablyhaving a peak at about 365 nm.
 18. A three-dimensional object formed bythe process of claim
 16. 19. A liquid radiation curable composition foradditive fabrication comprising: (a) a cationically polymerizablecomponent; (b) a (meth)acrylate component; (c) a cationicphotoinitiator; (d) a free-radical photoinitiator; (e) a filled matrix,further comprising a filled particle dispersion containing ananoparticle constituent made up of a plurality of silica nanoparticleshaving an average particle size of at least about 50 nanometers, and asolvent, and a microparticle constituent made up of a plurality ofinorganic microparticles; wherein the ratio by weight of themicroparticle constituent to the nanoparticle constituent is from about1:1 to about 12:1, wherein the filled particle dispersion has a particledispersion pH of greater than about 5.5.
 20. The liquid radiationcurable composition for additive fabrication of claim 19, wherein saidplurality of silica nanoparticles have an average particle size of fromabout 50 nanometers to about 100 nanometers; said plurality of inorganicmicroparticles have an average particle size of from about 0.2 micronsto 20 microns; and wherein the particle dispersion pH of the filledparticle dispersion is from 6.0 to about 7.5.
 21. The liquid radiationcurable composition for additive fabrication of claim 20, wherein thefilled matrix is present in an amount by weight, relative to the entirecomposition, of from about 50 wt % to about 70 wt %.
 22. The liquidradiation curable composition for additive fabrication of claim 21,wherein the ratio of the average particle size of the inorganicmicroparticles in the microparticle constituent to the average particlesize of the silica nanoparticles in the nanoparticle constituent is fromabout 6.46:1 to about 100:1; and the ratio by weight of themicroparticle constituent to the nanoparticle constituent is from about4:1 to about 8:1.
 23. The liquid radiation curable composition foradditive fabrication of claim 22, wherein the solvent is selected fromone or more of the group consisting of methyl ethyl ketone, isopropanol,an epoxide, an oxetane, and an acrylate.
 24. The liquid radiationcurable composition for additive fabrication of claim 23, wherein thesolvent is a 3,4-epoxycyclohexylmethyl3′,4′-epoxycyclohexanecarboxylate.
 25. The liquid radiation curablecomposition for additive fabrication of claim 24, wherein component (c)is an R-substituted aromatic thioether triaryl sulfonium or iodoniumtetrakis(pentafluorophenyl) borate cationic photoinitiator with atetrakis(pentafluorophenyl)borate anion and a cation of the followingformula (I):

wherein Y1, Y2, and Y3 are the same or different and wherein Y1, Y2, orY3 are R-substituted aromatic thioether with R being an acetyl orhalogen group.
 26. The liquid radiation curable composition for additivefabrication of claim 24, wherein component (c) is afluoroalkyl-substituted fluorophosphate with a cation of the followinggeneral formula (II):

wherein R¹, R², R³, R⁵ and R⁶ each independently represent an alkylgroup, a hydroxy group, an alkoxy group, an alkylcarbonyl group, anarylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group,an arylthiocarbonyl group, an acyloxy group, an arylthio group, analkylthio group, an aryl group, a heterocyclic hydrocarbon group, anaryloxy group, an alkylsulfinyl group, an arylsulfinyl group, analkylsulfonyl group, an arylsulfonyl group, a hydroxy(poly)alkyleneoxygroup, an optionally substituted amino group, a cyano group, a nitrogroup, or a halogen atom, R⁴ represents an alkyl group, a hydroxy group,an alkoxy group, an alkylcarbonyl group, an alkoxycarbonyl group, anacyloxy group, an alkylthio group, a heterocyclic hydrocarbon group, analkylsulfinyl group, an alkylsulfonyl group, a hydroxy(poly)alkyleneoxygroup, an optionally substituted amino group, a cyano group, a nitrogroup, or a halogen atom, m¹ to m⁶ each represent the number ofoccurrences of each of R¹ to R⁶, m¹, m⁴, and m⁶ each represent aninteger of 0 to 5, and m², m³, and m⁵ each represent an integer of 0 to4.